How do plants act fast to fight off infections?
Findings could inspire efforts to improve crop yields and combat global
hunger

Date:
October 27, 2021
Source:
Carnegie Institution for Science
Summary:
New work reveals a new mechanism by which plants are able to rapidly
activate defenses against bacterial infections. These findings could
inspire efforts to improve crop yields and combat global hunger.



FULL STORY ==========================================================================
New work led by Carnegie's Kangmei Zhaoand Sue Rhee reveals a new
mechanism by which plants are able to rapidly activate defenses against bacterial infections. This understanding could inspire efforts to improve
crop yields and combat global hunger.


========================================================================== "Understanding how plants respond to stressful environments is critical
for developing strategies to protect important food and biofuel crops
from a changing climate," Rhee explained.

Published in eLife, new work from Zhao and Rhee, along with Carnegie's
Benjamin Jinand Stanford University's Deze Kong and Christina Smolke,investigated how production of a plant defense compound called
camalexin is activated at the genetic level.

"Because plants grow in a fixed location, they can't flee from predators
or pathogens," Zhao explained. "Instead, they've evolved to produce
compounds that help them fight off invaders, among other functions."
Camalexin, like other plant metabolites, is synthesized by specialized
worker- proteins called enzymes that perform many of the cell's functional duties. When the plant is under environmental stress, it activates the
genes encoding these enzymes. The researchers set out to elucidate how
a plant cell can rapidly fire up the production line and respond to
external conditions or threats at the right time.

A cell's genetic material encodes the recipes for making these camalexin- producing enzymes and all the proteins that the cell could need to conduct
its necessary functions under a variety of conditions at every stage of
its life.

This is a lot of information. Which is why organization of the genetic
code in the cell is so crucial.

"Imagine a cell's genome is a massive library and each gene is a book,
and each chromosome is an extremely large shelf," Rhee said. "The cell has different mechanisms for quickly finding the gene it needs in this vast
array of information, so that it can be transcribed and translated to make
the encoded protein and respond to environmental conditions, including
threats and stress." These strategies include adding or removing tags
or marks in the packaging of all the genes and associated material -- collectively called chromatin -- which can enhance or inhibit expression
of particular genes. Sometimes, both activating and repressing elements
are present simultaneously, a phenomenon called bivalent chromatin.

Zhao, Rhee, and their colleagues were able to elucidate the existence of
a never-before-characterized type of bivalent chromatin -- they termed
it a kairostat, from the Greek "kairos," meaning at the right moment,
and "stat," meaning device -- which keeps the biosynthesis pathway for camalexin inactive until there is a pathogen signal. Their findings
indicate that both elements are needed to control the proper timing of
the plant's response to external stress.

"Camalexin and other defense compounds are often very expensive and
toxic for the plants to make. So, it's disadvantageous for plants to make
them all the time," said Zhao. "Plant scientists have known for a long
time that these defense compounds are made just in time when a plant is attacked by pests and pathogens. We now have a new handle on a molecular mechanism that enables this precise timing of camalexin production. This finding could inform strategies for fighting climate change and global
hunger, or even the synthesis of plant- derived medicines." Looking
ahead, the group wants to characterize all the proteins involved in establishing and removing epigenetic marks to identify more kairostats
and better understand their role in environmental responses and other
plant functions.

========================================================================== Story Source: Materials provided by
Carnegie_Institution_for_Science. Note: Content may be edited for style
and length.


========================================================================== Journal Reference:
1. Kangmei Zhao, Deze Kong, Benjamin Jin, Christina D Smolke, Seung Yon
Rhee. A novel bivalent chromatin associates with rapid induction
of camalexin biosynthesis genes in response to a pathogen signal
in Arabidopsis. eLife, 2021; 10 DOI: 10.7554/eLife.69508 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/10/211027085343.htm

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