Plant immunity (Introduction)
by David Turell 
, Tuesday, February 02, 2016, 17:17 (3216 days ago)
There are molecular recognition sensors which trigger molecular reactions and cascades to protect plants from pathogens:-http://www.the-scientist.com/?articles.view/articleNo/45201/title/Plant-Immunity/-"Plants have two basic immune pathways. First, a pattern recognition receptor (PRR) on the plant cell's surface recognizes pathogen-associated molecular patterns (PAMPs) released by invaders—say, the flagellar proteins from pathogenic bacteria. This jump-starts signaling pathways inside the cell that spur the production of reactive oxygen species (ROS) and antimicrobial compounds, which are secreted to combat the pathogen. PAMP-triggered pathways can also lead to changes in gene expression and hormone levels.-"But bacteria can interfere with PAMP-triggered immunity by injecting effector molecules into the plant cell. Intracellular plant protein complexes called nucleotide-binding domain, leucine-rich repeat receptors (NLRs) bind bacterial effectors and set off secondary immune cascades that boost the PAMP-triggered responses. NLR-binding can also lead to plant cell death, limiting the infection.-"Plant immune systems must integrate a diversity of factors to successfully fight off pathogens without harming the plant. Defense-related changes in hormone signaling, for example, can interfere with plant growth. Many species power down their immune systems at night, when growing ramps up. Plant immunity also fluctuates with changes in temperature, humidity, and light exposure, and is likely dependent on a plant's microbiota below and above the soil.-For the full story:-http://www.the-scientist.com/?articles.view/articleNo/45148/title/Holding-Their-Ground/-"Just like animals, plants have to fight off pathogens looking for an unsuspecting cell to prey on. Unlike animals, however, plants don't have mobile immune cells patrolling for invaders. “Every cell has to be an immune-competent cell,” says Jeff Dangl, who studies plant-microbe interactions at the University of North Carolina at Chapel Hill.-"Decades of work on model plants such as Arabidopsis thaliana have revealed robust cellular immune pathways. First, plasma membrane receptors recognize bits of pathogen and kick-start signaling cascades that alter hormone levels and immune-gene expression. This triggers the cell to reinforce its wall and to release reactive oxygen species and nonspecific antimicrobial compounds to fight the invaders. These responses can also be ramped up and prolonged by a second immune pathway, which can lead to localized plant cell death. Some plant defense compounds even manipulate bacterial communication. The polyphenol rosmarinic acid, for example, was recently found to disrupt a quorum-sensing pathway that Psuedomonas aeriginosa uses to form biofilms.-***-"Another important factor in a plant's resistance to pathogens is its microbiome. He's team has found that germ-free Arabidopsis plants express lower levels of many immune genes and exhibit impaired immune responses such as reactive oxygen species production compared to their microbe-colonized counterparts—findings that he hopes to publish this year. And Dangl's group recently reported that the Arabidopsis microbiome is shaped by the plant's hormones, especially salicylic acid.15-"But how these microbial communities interact with the plant immune system is still a mystery. Just as many microbiologists would like to know how the human body tells the good microbes from the bad, those studying plant immunity are trying to understand how plants make peace with beneficial inhabitants. “All of these microbes are going to have PAMPs,” says Dangl. “You have to know who your friends are.”-Comment: All sounds like automatic molecular responses, as I've noted before.
Plant immunity; new discoveries with complex enzymes
by David Turell , Monday, September 17, 2018, 23:18 (2257 days ago) @ David Turell
Plants can defend themselves with reactive oxygen:
https://www.sciencedaily.com/releases/2018/09/180917153612.htm
"Just like humans, plants have an immune system that helps them fight off infections. Plant immunity has some important differences: they don't make antibodies and can't fight off the same bug more quickly months or years later. However, plant cells can identify pathogens and react to them, often by producing a burst of reactive oxygen which is toxic to bacteria or fungi. Cells around an infected site will go into programmed cell death to seal off the disease.
"Gitta Coaker, professor in the Department of Plant Pathology at UC Davis and colleagues have now identified a key step in how plant cells respond to pathogens. They have identified a family of kinase enzymes that activate the enzymes that make reactive oxygen.
"It was known that plants can produce reactive oxygen, but not how different proteins coordinate activation of the reactive oxygen synthase," Coaker said.
"Every plant cell can respond to pathogens, Coaker said, through receptors on the cell surface that react to things like bacterial proteins. Plants have a large repertoire of these innate immune receptors: the small laboratory plant Arabidopsis, for example, has about 600 receptors that could respond to different pathogens.
"Plants also have receptors with similarity to "Toll-Like Receptors" or TLRs. These TLRs are similar to proteins found in insects and mammals that trigger responses to bacteria and other pathogens. TLRs were first discovered in plants by Professor Pamela Ronald of the UC Davis Department of Plant Pathology.
"Coaker's laboratory has now isolated an enzyme, SIK1, in Arabidopsis that is the "firing pin" of plant immunity. It connects the receptors that detect pathogens to the reactive oxygen that kills them.
"'This particular kinase works with and stabilizes others that converge on the enzyme that makes reactive oxygen," Coaker said. "We think this is a key step."
"When the researchers deleted SIK1, the plants were unable to make enough reactive oxygen and were more susceptible to infections."
Comment: Immunity processes are necessary from the appearance of any organism, or infections will run roughshod over then and they will not survive. Only design can do this.
Plant immunity; cellular isolation
by David Turell , Tuesday, April 14, 2020, 21:29 (1683 days ago) @ David Turell
Shutting off communication stops infections advance:
https://phys.org/news/2020-04-self-isolation-calm-onthe-cell-dilemma.html
"Self-isolation in the face of a marauding pathogen may save lives but it comes at the expense of life-sustaining essentials such as transport, communication and connectivity.
"This leaves decision makers with a dreadful dilemma as they judge when it's time to relax lockdown measures.
"New research suggests plants must balance similar trade-offs as they respond to pathogens that could rip through their defence cell by cell.
"Plant cells communicate with their neighbours by tunnel-like connections called plasmodesmata. This is one way that cells exchange information and resources.
"Plasmodesmata are lined by the same membrane that surrounds the cell and they allow molecules to move from one cell into the surrounding cells.
"When a cell perceives a threat like an invading fungus or bacteria, the plasmodesmata close over and the cells are temporarily isolated.
***
"They show that the cell wall material of fungus—called chitin—triggers different responses in the membrane that lines the plasmodesmal tunnels when compared to the responses it triggers in the membrane that surrounds the cell body.
"The signaling cascade in plasmodesmata triggers the production of a polysaccharide called callose that forces the plasmodesmal tunnel to close over and for the cells to isolate themselves.
"'This indicates that cells control their connectivity independently of other responses, although we don't yet know why this is," explains Dr. Christine Faulkner of the John Innes Centre.
"The study also finds that guard-like receptors that sit in the plasmodesmata are different from those that sit in the rest of the membrane, but both receptors use the same enzyme.
"'This is puzzling", says Dr. Faulkner, "but we also discovered that the mechanism of activation of this enzyme in the plasmodesmata is different to the mechanism used in the rest of the membrane. Thus, it seems that while both receptors use the same tool (the enzyme) to transmit a signal, they use it differently for different purposes."
"The requirement for specific signaling in the plasmodesmal part of the cell membrane suggests that the vital processes requiring cell-to-cell connectivity must be regulated independently of immune response."
Comment: Plants are built so differently than animals with circulations, they must use different approaches to immunity. Their responses are biochemically just as complex as animals. Design required
Plant immunity; more discoveries
by David Turell , Friday, August 07, 2020, 19:34 (1568 days ago) @ David Turell
This one is in legumes:
https://phys.org/news/2020-08-distinguish-beneficial-microbes.html
"Legume plants know their friends from their enemies, and now we know how they do it at the molecular level. Plants recognize beneficial microbes and keep harmful ones out, which is important for healthy plants production and global food security. Scientists have now discovered how legumes use small, well-defined motifs in receptor proteins to read molecular signals produced by both pathogenic and symbiotic microbes. These remarkable findings have enabled the researchers to reprogram immune receptors into symbiotic receptors, which is the first milestone for engineering symbiotic nitrogen-fixing symbiosis into cereal crops.
"Legume plants fix atmospheric nitrogen with the help of symbiotic bacteria, called Rhizobia, which colonize their roots. Therefore, plants have to be able to precisely recognize their symbiont to avoid infection by pathogenic microbes. To this end, legumes use different LysM receptor proteins located on the outer cell surface of their roots. In the study published in Science, an international team of researchers led by Aarhus University show that pathogenic (chitin) or symbiotic signaling molecules (Nod factors) are recognized by small molecular motifs on the receptors that direct the signaling output towards either antimicrobial defense or symbiosis.
"All land plants have LysM receptors that ensure detection of various microbial signals, but how a plant decides to mount a symbiotic or an immune response towards an incoming microbe is unknown.
***
"...the researchers identified previously unknown motifs in the LysM1 domain of chitin and Nod factor receptors as determinants for immunity and symbiosis. "It turns out that there are only very few, but important, residues that separate an immune from a symbiotic receptor and we now identified these and demonstrate for the first time that it is possible to reprogram LysM receptors by changing these residues," says Kasper Røjkjær Andersen.
Comment: I again assume these mechanisms were designed when these plants evolved to protect them for survival. If an attempt is made to survive by chance arrival of protective mechanisms makes no sense. But then again, Darwinism makes no sensed.
Plant immunity; more discoveries
QUOTE: "All land plants have LysM receptors that ensure detection of various microbial signals, but how a plant decides to mount a symbiotic or an immune response towards an incoming microbe is unknown.
DAVID: I again assume these mechanisms were designed when these plants evolved to protect them for survival. If an attempt is made to survive by chance arrival of protective mechanisms makes no sense. But then again, Darwinism makes no sense.
QUOTE: Plants recognize beneficial microbes and keep harmful ones out….
These plants appear to do exactly what - in your new, Darwinian "error theory" - you think your God does, and what Darwin thinks natural selection does: “mistakes” (mutations) arrive by chance, and your God or Nature selects the beneficial ones (your new theory); and here we have microbes arriving by chance and plants selecting the beneficial ones. I propose that this is a sign of plant (cellular) intelligence. And as your God is the maker of all things, he would have deliberately created their intelligence, just as he would have deliberately created the whole system that provides both beneficial and harmful “mutations” throughout the ever changing history of life on Earth. Intelligent design? Yes, if God exists he would have designed the intelligence which in turn would have designed organismal responses to randomly changing conditions and events.
Plant immunity; more discoveries
by David Turell , Saturday, August 08, 2020, 19:21 (1567 days ago) @ dhw
QUOTE: "All land plants have LysM receptors that ensure detection of various microbial signals, but how a plant decides to mount a symbiotic or an immune response towards an incoming microbe is unknown.
DAVID: I again assume these mechanisms were designed when these plants evolved to protect them for survival. If an attempt is made to survive by chance arrival of protective mechanisms makes no sense. But then again, Darwinism makes no sense.
QUOTE: Plants recognize beneficial microbes and keep harmful ones out….
dhw: These plants appear to do exactly what - in your new, Darwinian "error theory" - you think your God does, and what Darwin thinks natural selection does: “mistakes” (mutations) arrive by chance, and your God or Nature selects the beneficial ones (your new theory); and here we have microbes arriving by chance and plants selecting the beneficial ones. I propose that this is a sign of plant (cellular) intelligence. And as your God is the maker of all things, he would have deliberately created their intelligence, just as he would have deliberately created the whole system that provides both beneficial and harmful “mutations” throughout the ever changing history of life on Earth. Intelligent design? Yes, if God exists he would have designed the intelligence which in turn would have designed organismal responses to randomly changing conditions and events.
For me God exists and codes instructions for organisms to follow.
Plant immunity; more discoveries
by David Turell , Monday, August 24, 2020, 18:30 (1551 days ago) @ David Turell
How tobacco plants protect again weevils:
https://phys.org/news/2020-08-strigolactones-tolerance-weevils-tobacco.html
"Not only animals, but also plants have different hormones that control various processes in the body. One class of these signaling substances that were only recognized as hormones quite recently are strigolactones. In plants, they are involved in shoot formation inhibit further branching of the stem. As scientists at the Max Planck Institute for Chemical Ecology have now discovered, a change in the signaling pathway of strigolactones influences processes regulated by other plant hormones, and—as a consequence—a plant's defense against herbivores.
***
"The results of the study demonstrate that although strigolactones do not directly regulate defenses against the weevil, they indirectly use the existing hormonal regulatory networks, here via jasmonates and auxins, to produce defensive substances that enable the plant to tolerate this herbivore inside its stem.
"'In short, 'defenses' damage the herbivores, while 'tolerance' traits decrease the damage that herbivore attack causes. It is in the realm of tolerance traits that makes the discovery that these hormones fine-tune plant defense via their crosstalk with other hormones, such as jasmonates and auxins, so exciting," says Ian Baldwin, director of the Department of Molecular Ecology where the investigations have been carried out.
"The researchers propose that strigolactones in the plant represent a kind of switch between defense against and tolerance of herbivores, a hypothesis that—if confirmed—would also offer new interesting approaches for plant breeding."
Comment: Complex defenses with several different proteins require design to put such a system together, and must be present at the start of the life of the specific plant type.
Plant immunity; more discoveries
by David Turell , Wednesday, August 26, 2020, 21:51 (1549 days ago) @ David Turell
How plants protect themselves by closing their pores:
https://phys.org/news/2020-08-door-infection.html
"Plants have a unique ability to safeguard themselves against pathogens by closing their pores—but until now, no one knew quite how they did it. Scientists have known that a flood of calcium into the cells surrounding the pores triggers them to close, but how the calcium entered the cells was unclear.
***
"A new study by an international team including University of Maryland scientists reveals that a protein called OSCA1.3 forms a channel that leaks calcium into the cells surrounding a plant's pores, and they determined that a known immune system protein triggers the process.
***
"Plant pores—called stomata—are encircled by two guard cells, which respond to calcium signals that tell the cells to expand or contract and trigger innate immune signals, initiating the plant's defense response. Because calcium cannot pass directly through the guard cell membranes, scientists knew a calcium channel had to be at work. But they didn't know which protein acted as the calcium channel.
"To find this protein, the study's lead author, Cyril Zipfel, a professor of molecular and cellular plant physiology at the University of Zurich and Senior Group Leader at The Sainsbury Laboratory in Norwich, searched for proteins that would be modified by another protein named BIK1, which genetic studies and bioassays identified as a necessary component of the immune calcium response in plants.
"When exposed to BIK1, one protein called OSCA1.3 transformed in a very specific way that suggested it could be a calcium channel for plants. OSCA1.3 is a member of a widespread family of proteins known to exist as ion channels in many organisms, including humans, and it seems to be specifically activated upon detection of pathogens.
***
"Erwan Michard, a visiting assistant research scientist in Feijó's lab and co-author of the paper, conducted experiments that revealed BIK1 triggers OSCA1.3 to open up a calcium channel into a cell and also explained the mechanism for how it happens.
"BIK1 only activates when a plant gets infected with a pathogen, which suggests that OSCA1.3 opens a calcium channel to close stomata as a defensive, immune system response to pathogens."
Comment: Another complex mechanism that had to be designed for the original plants when they first evolved. Chance evolution cannot arrange for simultaneously required developments
Plant immunity; more discoveries
by David Turell , Saturday, May 21, 2022, 17:05 (916 days ago) @ David Turell
The latest study:
https://www.sciencedaily.com/releases/2022/05/220520132832.htm
"Key players in these plant immune responses are so-called immune receptors, which detect the presence of molecules delivered by foreign microorganisms and set in motion protective responses to repel the invaders.
"A subset of these immune receptors harbours specialized regions known as toll-interleukin-1 receptor (TIR) domains and function as enzymes, special proteins that break down the molecule nicotinamide adenine dinucleotide (NAD+), a highly abundant, multi-functional small molecule found in all living cells. Breakdown of NAD+, in turn, activates additional immune proteins, ultimately culminating in the so-called "hypersensitive response," a protective mechanism that leads to the death of plant cells at sites of attempted infection as an effective way to protect the plant as whole. However, studies have shown that breakdown of NAD+, while essential, is not sufficient for plant protection, suggesting that additional mechanisms must be involved.
***
"Using structural analysis, the authors could show that TIR proteins form different multi-protein structures for breakdown of NAD+ or RNA/DNA, explaining how one and the same protein can carry out two roles. To cleave the RNA/DNA molecules, the TIR proteins follow the contours of the RNA/DNA strands and wind tightly around them like pearls on a string. The ability of TIR proteins to form two alternative molecular complexes is a characteristic of the entire immune receptor family. The exact shape of the TIR proteins thus dictates the respective enzyme activity. (my bold)
***
"Using analytical chemistry, the scientists could identify the molecules as cAMP/cGMP (cyclic adenosine monophosphate/cyclic guanosine monophosphate), so-called cyclic nucleotides that are present in all kingdoms of life. Intriguingly, rather than the well-characterized 3',5'-cAMP/cGMP, the authors analysis showed that the TIR domains were triggering the production of the so-called non-canonical 2',3'-cAMP/cGMP, enigmatic "cousins," whose precise roles have thus far been unclear. When they reduced TIR-mediated production of 2’,3’-cAMP/cGMP, cell death activity was impaired, demonstrating that the 2',3'-cAMP/cGMP molecules are important for the plant immune response. (my bold)
"If 2',3'-cAMP/cGMP promote cell death in plants in response to infection, then it stands to reason that their levels would be kept tightly in check. Indeed, the authors discovered that a known negative regulator of TIR function in plants, NUDT7, acts by depleting 2',3'-cAMP/cGMP. Similar negative regulators are released by certain pathogenic microorganisms during infection inside plant cells, and the scientists could show that these pathogen proteins also deplete 2',3'-cAMP/cGMP. This suggests that invading microorganisms have evolved clever strategies to disarm the 2',3'-cAMP/cGMP-dependent plant defence mechanism for their own benefit." (my bold)
Comment: note the comments about the universality of these immunity molecules. This is a clear demonstration of the relationships in the biochemical continuity of evolution. One of my bolds shows any process that produces a dangerous process as initiating cell death must have tight controls. To have this properly designed, it is obvious the process for death and its controls must be designed all at once, never stepwise. Another amazing aspect (in bold)is
shape shifting molecules control enzyme activity. Not by chance.
Plant immunity; fighting off bacteria
by David Turell , Tuesday, May 31, 2022, 19:31 (906 days ago) @ David Turell
A battle back and forth:
https://phys.org/news/2022-05-invading-pathogens-cells-defenses.html
"Many disease-causing bacteria are able to inhibit the defense mechanisms in plants and thus escape dissolution by the plant cell, a process known as xenophagy. Animal and human cells have a similar mechanism whereby the cell's defenses "eat" invading bacteria—yet some bacteria can inhibit the process. An international research team has now described the inhibition of xenophagy in plants for the first time.
***
"Cells must constantly adapt the proteins inside them to changing functions and to influences from their surroundings. "Constant protein degradation is unavoidable, otherwise the cell becomes cramped and runs out of material," explains Suayb Üstün, whose working group studies these strictly regulated degradation processes. When the cell has to degrade large protein complexes, insoluble aggregates or entire organelles, it usually uses a process known as autophagy, literally "eating itself." "Animal and human cells also sometimes use this method of degradation when they want to eliminate invaders such as pathogenic bacteria. In this case, the process is also called xenophagy—eating the stranger," says the scientist.
"But the arms race between host and pathogen does not end there. Some bacteria have developed proteins that block the autophagy machinery directed at them. This gives them an advantage and they can spread further. "This state of research has been known for several years in human cells. With plants, we haven't got that far yet. There is an important difference between autophagy in plant and animal cells—in plants, pathogenic bacteria do not penetrate the cells. They stay in the extracellular space," says Üstün. This is the case, for example, with the bacterium Xanthomonas, which causes wilting and rotting of leaves, stems and fruits in a whole range of plants and also affects tobacco, the model plant studied by the research team.
"'Xanthomonas bacteria introduce an effector into the plant cells. We found that this suppresses an important component of the autophagy machinery. This allows Xanthomonas to spread further," Üstün explains. "However, the plant in turn produces a protein that degrades the effector by autophagy." This is the first evidence of antimicrobial xenophagy in plant-bacteria interactions, he says. Üstün adds that "an interesting aspect of this is that the proteins involved, such as the Xanthomonas effector and the components of the autophagy machinery, are very similar in humans and plants, although they are attacked by different bacterial pathogens." Biologists observe that some proteins have been strongly conserved in very different organisms over the course of evolution."
Comment: No surprise. Of course, immune mechanisms are always in a battle. And th comparative systems suggest convergent evolution.
Plant immunity; fighting off bark beetles
by David Turell , Sunday, October 02, 2022, 22:34 (781 days ago) @ David Turell
The tress produce obnoxious fragrances:
https://www.the-scientist.com/news-opinion/pine-trees-fragrances-help-neighbors-battle-...
"The herbivores in this study were large pine weevils (Hylobius abietis L.), common pests in European coniferous forests that feed on tree bark and kill young seedlings. Clearcutting of forests amplifies the beetles’ impact; weevils reproduce in the newly created stumps and ravage the seedlings that grow in their place.
"However, conifers aren’t completely defenseless against these dime-sized invaders. Much like kitchen herbs whose scent becomes more potent when crushed or broken apart, Scotch pine (Pinus sylvestris) and other trees emit fragrant molecules when herbivores chew through their bark. These molecules, known as herbivore-induced plant volatiles (HIPVs), repel the herbivore and attract its predators.
"Additionally, Hao Yu, a plant ecophysiologist at the University of Eastern Finland, knew that some tree species use these volatile compounds to communicate with one another, allowing for neighbors of a besieged plant to increase their defenses against whatever animal is attacking them. However, this behavior had never been studied in conifers, which are famous for their belowground networks of fungal communication.
***
"The researchers found that receiver saplings exposed to the HIPVs of infested emitter plants were more resistant to pine weevil damage than those not exposed to infested saplings. These exposed plants emitted more volatiles and boasted more robust resin ducts with a greater cell count. Together, the emission of HIPVs and increased resin production are a strong deterrent to invading bugs. Yu and his colleagues also found higher rates of photosynthesis (which would enable plants to generate the carbon resources needed for volatile and resin production), and increased stomatal conductance, which allows for more airflow to support photosynthesis, in receiver plants exposed to infested plants.
"Combined, these results indicate that HIPVs are a call-to-arms for neighboring pine saplings, telling them to gear up for battle, says biologist Jörg-Peter Schnitzler of Helmholtz Munich Research Center who wasn’t involved in the study.
"The infested tree “is sending out a so-called ‘cry for help,’ and its neighbors are somehow sensing it,” Schnitzler says. “And then [the neighbors] are priming their defense and are more active in defending against an upcoming enemy. That’s really exciting to see./”
Comment: I left out the description of how was studied with saplings in the lab with infected and uninfected trees. The question, of course, is how this developed, naturally or by God.
Plant immunity; fighting off bacteria
by David Turell , Sunday, October 15, 2023, 18:32 (404 days ago) @ David Turell
Using salicylic acid:
https://phys.org/news/2023-10-biologists-salicylic-acid-rna-antiviral.html
"Plant viruses threaten the health of their hosts, can spread swiftly and globally, and challenge agricultural productivity. When viruses successfully infect plants, the infection often spreads through the entire organism. Well, not entirely: One small group of indomitable cells still holds out, the stem cells within the shoot tip. This small group of cells generates all plant tissues above ground, including the next plant generation, and for reasons still poorly understood, viruses are unable to proliferate in these cells.
***
"Using this dynamic, semi-quantitative approach, the researchers observed that Turnip mosaic virus—their plant model virus of choice—spreads in their model plant Arabidopsis thaliana, arrives at the stem cells within the shoot tip , and even enters these cells, but is then quickly excluded. "Surprisingly, these cells are really good at driving the virus out."
"Past work on a close relative of tobacco had provided clues that RNA interference—a pathway that inhibits virus proliferation in plants and many animals—plays a role in virus exclusion in plants. In the search for the defense's molecular bases, the researchers therefore screened Arabidopsis mutant plants that miss certain components of the RNA interference pathway. In addition, they studied plants deficient in salicylic acid, a key plant defense hormone.
"Through a series of targeted experiments, the researchers were able to see that during virus infection, salicylic acid production is activated. "The plant recognizes the virus and sets off salicylic acid as an alarm bell." Salicylic acid in turn activates a key factor in RNA interference amplification, called RDR1. RDR1 ramps up production of double-stranded RNA from viral RNA, giving plants more virus-specific sequences to direct the defense mechanism against the invading virus.
"'In the fight against Turnip mosaic virus, both salicylic acid and RDR1 are necessary to expel the virus from the stem cells—however, RDR1 is not produced within the stem cells themselves, but in the tissue below the stem cells and in the vasculature," Incarbone adds.
***
"But every virus is different. In the fight against other viruses, salicylic acid and RDR1 are activated but not necessarily required. "Based on our experiments with other viruses we can, however, conclude that RNA interference is always necessary to defend stem cells from infection.'"
Comment: plant immunity is like ours using a part of the virus to make an antibody.
Plant immunity; fighting off bacteria II
by David Turell , Sunday, December 10, 2023, 15:31 (348 days ago) @ David Turell
Little water balloons:
https://www.sciencealert.com/weve-been-wrong-for-more-than-a-century-about-these-little...
"It was thought that these tiny balloons protected the plants against dangers like drought and salt. Not so, says a new study; in fact, they're designed to ward off different kinds of dangers, in the form of pests and disease.
"The discovery was made by researchers who wanted to explore the original hypothesis in more detail. To that end, they cultivated mutant quinoa plants and ice plants without the usual covering of balloons (technically known as epidermal bladder cells or EBCs).
"'Whether we poured salt water on the mutant plants without bladder cells or exposed them to drought, they performed brilliantly and against expectations," says biologist Max Moog, from the University of Copenhagen in Denmark. "So, something was wrong."
"'On the other hand, we could see that they were heavily infested with small insects – unlike the plants covered with bladder cells."
"The researchers suggest that the miniature balloons act as a block to pests, and that when tiny creatures such as thrips try and take a bite of the plant, they end up with a mouthful of toxic solution carried by the EBCs.
"Further analysis of the contents of the EBCs revealed one of the ingredients inside them was oxalic acid, which is poisonous to pests. However, there was no more salt present than in surrounding cells, suggesting the idea that these balloons acted as overflow chambers for excess salt was incorrect.
"What's more, the team also observed that the mutant, balloon-less plants were more vulnerable to Pseudomonas syringae, the cause of one of the most common bacterial diseases in plants. This could well be down to the way the balloons cover the stomata on the leaves of plants, which is often the route bacteria use to invade.
***
"There's no doubt plants such as these are highly resistant to abiotic stressors like drought and salt, but it seems that the protection isn't from these EBCs. Instead, it's biotic stressors that the balloons guard against."
Comment: epidermal balloons are a neat trick, oxalic acid another one. How would these plants survive if this mechanism was not evolved? Step-by-step or by chance mutations? Not likely. Design is the answser.
Plant immunity; fighting off fungus
by David Turell , Saturday, December 30, 2023, 19:31 (328 days ago) @ David Turell
Implant some RNA:
https://www.sciencedaily.com/releases/2023/12/231221012831.htm
UC Riverside scientists have discovered a stealth molecular weapon that plants use to attack the cells of invading gray mold.
***
A new paper in the journal Cell Host & Microbe describes how plants send tiny, innocuous-seeming lipid "bubbles" filled with RNA across enemy lines, into the cells of the aggressive mold.
Once inside, different types of RNA come out to suppress the infectious cells that sucked them in.
***
Previously, Jin's team discovered that plants are using the bubbles, technically called extracellular vesicles, to send small RNA molecules able to silence genes that make the mold virulent.
Now, the team has learned these bubbles can also contain messenger RNA, or mRNA, molecules that attack important cellular processes, including the functions of organelles in mold cells.
"These mRNAs can encode some proteins that end up in the mitochondria of the mold cells. Those are the powerhouses of any cells because they generate energy," Jin explained.
"Once inside, they mess up the structure and function of the fungal mitochondria, which inhibits the growth and virulence of the fungus."
It isn't entirely clear why the fungus accepts the lipid bubbles.
***
The strategy is an efficient one for the plants, because one mRNA molecule can have an outsized effect on the fungus.
"The beauty of delivering mRNA, instead of other forms of molecular weapons, is that one RNA can be translated into many copies of proteins. This amplifies the effect of the mRNA weapon," Jin said.
Mold also uses these same lipid bubbles to deliver small, damaging RNAs into the plants they are infecting to suppress host immunity, an ability developed as part of a co-evolutionary arms race.
Comment: part of the design must include a mechanism that prevents these mRNA's from damaging the plant itself. Stepwise development could result in severe mortality during the process. Direct design answers the problem.