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New Achievement: Small RNA Regulates Rice Disease-Resistance Response

Key Points: Nature Plants, Nature’s series, published online the research progress in small RNA regulating rice disease-resistance response on 1st, March. The article titled “Transposon-derived small RNA is responsible for modified function of WRKY45 locus” revealed that WRKY45-1, one of the two alleles of WRKY45 locus, could produce small RNA, so the two alleles of WRKY45 locus manifested opposite functions in the resistance of xanthomonas oryzae. The progress was made by the rice team of the state key laboratory of genetic improvement in HZAU.

Diseases are one of the major factors that affect crop production. The research group of rice disease resistance, led by Professor Wang Shiping, takes xanthomonas oryzae—the most harmful bacterial disease for rice as their object. Also they have dedicated themselves to the research of rice disease-resistance mechanism for a long time. The research group has made progress in the regulatory mechanism of rice disease resistance recently.

Previous studies show thatWRKY45 is an important quantitative resistance locus during the process of rice disease resistance. The locus has two different alleles, WRKY45-1 and WRKY45-2. The former resists xanthomonas oryzae while the latter accelerates it. For further explanation, the group has carried out many researches. It is discovered that the intron of WRKY45-1 gene is inserted with transposon(repetitive DNA sequences in genome), from which many partly overlapping small RNAs are generated during the genetic expression of WRKY45-1.Those small RNAs accelerate the methylation of ST1 gene intron and therefore restrain the genetic expression of ST1 at transcriptional level and reduce its function. ST1 gene is an

important gene in the disease-resistance signal transduction pathway regulated by WRKY45.Restriction of the genetic expression of ST1 makes disease-resistance response disappear and then, rice gets xanthomonas oryzae. Because intron in WRKY45-2 gene is not inserted with transposon, the genetical expression of WRKY45-2 gene does not generate small RNA. As a result, ST1 has a normal expression and rice is resistant to xanthomonas oryzae.

The findings mentioned above demonstrate the natural variation and functional differences of WRKY45 locus are due to the generation of small RNA, and reveal for the first time the molecular mechanism of small RNA regulating xanthomonas oryzae. What is more, they broaden people’s knowledge about the regulatory function of small RNA, and deepen their understanding of interactional mechanism between plants and pathogenic bacteria.

In addition, transposable elements (transposon is one kind of them) are a kind of unsteady DNA that largely exists in the genome of animals and plants. For example, about 40% of rice’s genome and about 85% of maize’s genome are transposable elements. Without control, transposable elements will always have changeable positions and increasing numbers in the genome. It is known that transposable elements are an important source of small RNA in all species. Those small RNA impede the expression of transposable elements through RNA-mediating DNA methylation, stabilize genome and enable it to function normally. But, people are not clear whether those small RNAs restrain the genetic expression of transposable elements in every physiological activity. Researchers in HZAU, for the first time, demonstrate the small RNA’s involvement in negative

regulatory disease-resistance response, which lays a foundation for the large-scale research on the effects of the transposable elements-derived small RNA in regulating every physiological activity.

The first writer of this research is Dr. Zhang Haitao, research associate of disease-resistance group, and the corresponding writer is Professor Wang Shiping. The research is funded by Natural Science Foundation of China (31471575, 31200912) and 973 Project (2012CB114005).

(By Yang Kaiyan)