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.