Natures wonders: parasite controls plant's defense (Introduction)

by David Turell , Thursday, January 18, 2018, 14:59 (2499 days ago) @ David Turell

An obligate parasite's amazing ability to block a plant's defense:

https://www.sciencedaily.com/releases/2018/01/180103132751.htm

"Dodder, a parasitic plant that causes major damage to crops in the US and worldwide every year, can silence the expression of genes in the host plants from which it obtains water and nutrients. This cross-species gene regulation, which includes genes that contribute to the host plant's defense against parasites, has never before been seen from a parasitic plant.

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"'Dodder is an obligate parasite, meaning that it can't live on its own," said Michael J. Axtell, professor of biology at Penn State and an author of the paper. "Unlike most plants that get energy through photosynthesis, dodder siphons off water and nutrients from other plants by connecting itself to the host vascular system using structures called haustoria. We were able to show that, in addition to the nutrients that flow into dodder from the host plant across the haustoria, dodder passes microRNAs into its host plant that regulate the expression of host genes in a very direct way."

"MicroRNAs are very short bits of nucleic acid -- the material of DNA and RNA -- that can bind to messenger RNAs that code for protein. This binding of microRNA to messenger RNA prevents the protein from being made, either by blocking the process directly or by triggering other proteins that cut the messenger RNA into smaller pieces. Importantly, the small remnants of the messenger RNA can then function like additional microRNAs, binding to other copies of the messenger RNA, causing further gene silencing.

"'Dodder seems to turn on the expression of these microRNAs when it comes into contact with the host plant," said James H. Westwood, professor of plant pathology, physiology, and weed science at Virginia Tech and another author of the paper. "What was really interesting is that the microRNAs specifically target host genes that are involved in the plant's defense against the parasite."

"When a plant is attacked by a parasite it initiates a number of defense mechanisms. In one of these mechanisms, similar to blood clotting after a cut, the plants produce a protein that clots the flow of nutrients to the site of the parasite. MicroRNA from dodder targets the messenger RNA that codes for this protein, which then helps to maintain a free flow of nutrients to the parasite. The gene that codes for this clotting protein has a very similar sequence across many plant species, and the researchers showed that the microRNA from dodder targets regions of the gene sequence that are the most highly conserved across plants.
Because of this, dodder can probably silence this clotting protein in, and therefore parasitize, a wide variety of plant species."

Comment: The evolution of this arrangement must have been stepwise with the Dodder partially independent until it worked out a way to silence the plant's defenses and then become totally obligate. Living organisms show purposeful behavior. I think that was programmed into life when life originated. God at work.