Scientists Uncover New Antiviral Defense Mechanism In Rice

Chinese researchers have revealed a new antiviral mechanism in rice, a discovery that could boost control against viral epidemics and guarantee food security.

AsianScientist (Apr. 10, 2017) – A decoy protein could be the secret to enhancing the antiviral response in rice. These findings, published in Nature Plants, could help to ensure food security by aiding the development of virus-resistant rice strains.

Rice stripe virus (RSV) is one of the most destructive pathogens for rice plants, and has been implicated in numerous epidemics since it was first identified in Japan in 1897. Understanding the mechanisms of anti-RSV defense in rice will help to control viral epidemics and guarantee food security.

Over the past decade, microRNAs (miRNAs) have been identified as key players in plant-microbe interactions. When incorporated into RNA-induced silencing complexes (RISCs), miRNAs promote the slicing or translational repression of their corresponding target transcripts.

In RSV-infected rice, it is known that certain miRNAs are bound to a protein called AGO18. Therefore, understanding the roles that miRNAs and AGO18 play in anti-RSV defense are indispensable for engineering virus-resistant crops.

To understand the anti-RSV response in plants, researchers from Professor Cao Xiaofeng’s group at the Institute of Genetics and Developmental Biology of the Chinese Academy of Sciences and Professor Li Yi’s group at Peking University studied the levels of both miR-528 and AGO18 during the course of an RSV infection.

They found that miR-528 negatively regulates viral resistance in rice through association with AGO1-containing RISCs, cleaving L-ascorbate oxidase messenger RNA and thereby reducing ascorbate oxidase-mediated accumulation of reactive oxygen species.

In rice infected with RSV, miR-528 is suppressed by AGO18, leading to the release of ascorbate oxidase and higher basal reactive oxygen species. Credit: Institute of Genetics and Developmental Biology, Chinese Academy of Sciences.

In addition, they found that miR-528 could be specifically recruited by AGO18 after RSV infection. Intriguingly, AGO18 is a decoy AGO protein and is incapable of slicing target transcripts. They further showed that AGO18 competes with AGO1 for miR528, thereby releasing the target of miR-528 target from slicing or translational repression.

Taken together, the results show that miR-528 is preferentially sequestered by cleavage-defective AGO18 during viral infection. This in turn leads to elevated ascorbate oxidase activity and higher basal reactive oxygen species accumulation, ultimately enhancing the antiviral response.

This study has unearthed an antiviral defense mechanism that is boosted through suppression of a miRNA that negatively regulates viral resistance. This mechanism could be manipulated by plant breeders to develop virus-resistant crops, the researchers suggest.

The article can be found at: Wu et al. (2017) ROS Accumulation and Antiviral Defense Control by MicroRNA528 in Rice.


Source: Chinese Academy of Sciences.
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