Two-faced orchestrator: Tis gene regulates positive and negative immune responses in plants
In a discovery important for agriculture and food safety, scientists
report the genetic regulation of a model plant's immune response

Date:
March 3, 2022
Source:
Tokyo University of Science
Summary:
The mechanism of plant defense mediated by the non-expressor
of pathogenesis-related (NPR) genes in monocots (plants having a
single embryonic leaf) is not well-documented. Now, scientists have
discovered how the NPR family of genes regulate immune responses in
the model monocot Brachypodium distachyon. These findings provide a
blueprint for plants' defense systems and might contribute to more
research towards resilient crop species, boosting pesticide-free
cereal crop cultivation.



FULL STORY ==========================================================================
In a discovery important for agriculture and food safety, scientists
report the genetic regulation of a model plant's immune response.


==========================================================================
The mechanism of plant defense mediated by the non-expressor of
pathogenesis- related (NPR) genes in monocots (plants having a single
embryonic leaf) is not well-documented. Now, scientists from Tokyo
University of Science have discovered how the NPR family of genes regulate immune responses in the model monocot Brachypodium distachyon. These
findings provide a blueprint for plants' defense systems and might
contribute to more research towards resilient crop species, boosting pesticide-free cereal crop cultivation.

Plants can be largely divided into dicotyledonous and monocotyledonous
ones.

These groups, apart from differing in their embryonic structure, have
numerous other distinguishing factors. Which is why, it's quite possible
that their immune responses to certain threats would be different as well.

Immune responses in plants? Leaves you confused? Well, though their immune systems are structured and function much differently than ours, plants,
like humans, do respond to external threat. These immune responses have
been studied extensively in dicot models, but lesser so in monocots.

The non-expressor of pathogenesis-related (NPR) family of genes are
known to control defensive signaling during a pathogen attack. In
Arabidopsis thaliana, a dicot, NPR1 (AtNPR1) serves as a binding site for salicylic acid (SA) and interacts with the TGA group of transcription
factors (TFs)-which are responsible for turning genes 'on' or 'off'
as needed. This activates defense genes, such as pathogenesis-related
protein 1 (PR-1), which ultimately control the plant's immunological
response. Does this happen in monocots as well? A research team, led
by Prof. Gen-ichiro Arimura from Tokyo University of Science in Japan
decided to find out.

They knew that some monocots, like rice and wheat, display a similar NPR1- mediated immune response on facing a pathogen attack. However, the team believed that other monocots may respond differently, and also wanted
to investigate other NPRs, such as AtNPR3/AtNPR4, which might have the
opposite effect of NPR1. Hence, Prof. Arimura and his colleagues chose
to investigate NPR function and immune response in the model monocot Brachypodium distachyon, often known as the southern duckweed.

Their study, which was published in The Plant Journal, explains how
NPR genes in B. distachyon regulate TGA-promoted transcription of defense-responsive genes.

The researchers first identified and cloned sequences of monocot B.

distachyon's NPR genes-BdNPR1, 2, and 3-which were similar to the NPR
sequences of other dicot species, including Arabidopsis. On methyl
salicylate treatment, the expression of BdNPR2 rose significantly,
but not BdNPR1/BdNPR3, indicating its positive role in plant defense
response. The researchers also confirmed that one of the BdNPRs (BdNPR2) activated BdTGA-1 in B. distachyon (just like other plants), by observing
gene expression and molecular interactions in B.

distachyon protoplasts. These experiments revealed that BdTGA1 and
BdNPR2 interacted with each other to upregulate PR-1 expression, thereby cementing the role of NPR2 in B. distachyon's immune response.

Was this response mediated by SA? Another pertinent question, which the
team answered by creating a created a mutant NPR2 gene. Prof. Arimura
points out: "Certain amino acid residues-especially those of arginine
(Arg)-are responsible for SA binding in Arabidopsis NPRs. So, our mutant
NPR2 was missing a specific arginine residue-Arg468." This mutant was less effective than the normal wild- type NPR2 at increasing PR-1 expression, implying that Arg468 was critical for SA binding on NPR2, which, in
turn, upregulated PR-1. Interestingly, their experimental assays also
found that BdNPR1 suppressed this upregulation, suggesting its role as
an immune inhibitor in B. distachyon.

Prof. Arimura sums it all up for us. "When the plant is in a healthy
state, BdNPR1 may stop BdNPR2 from activating BdTGA1, keeping the PR1
gene turned off.

But when the plant is attacked by a pathogen, SA levels rise and
stimulate BdNRP2 expression, which then cascades, and 'turns on' the
PR1 gene." Surprised by how functionally unique BdNRP2 is, Prof. Arimura explains that the "sequence similarities between NPR2 from B. distachyon
and other plants does not affect their functions which are distinctively different for every plant species." But how does this genetic research translate into real-life applications? Many important crops, such as
wheat and rice, are monocots. These plants, which are susceptible to
microbial pathogens and pests, are treated with pesticides to avoid
damage. The pesticides then cause environmental degradation. "This
vicious cycle can be broken by understanding monocots' defense systems,
and addressing their susceptibility in a more sustainable way, with pesticide-free cultivation," says Prof. Arimura, who hopes this research
will be used to further plant biotechnology. It puts us one step closer
to resolving the global environment and food security issues, allowing
us to work towards a more sustainable society.

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


========================================================================== Journal Reference:
1. Kohei Shimizu, Hitomi Suzuki, Takuya Uemura, Akira Nozawa, Yoshitake
Desaki, Ryosuke Hoshino, Ayako Yoshida, Hiroshi Abe, Makoto
Nishiyama, Chiharu Nishiyama, Tatsuya Sawasaki, Gen‐ichiro
Arimura. Immune gene activation by NPR and TGA transcriptional
regulators in the model monocot Brachypodium distachyon. The Plant
Journal, 2022; DOI: 10.1111/ tpj.15681 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/03/220303141216.htm

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