RNA-dependent RNA polymerase 6 (RDR6) is a core component of the small RNA biogenesis pathway, but its function in meiosis is unclear. Here, we report a new allele of OsRDR6 (Osrdr6-meiosis [Osrdr6-mei]), which causes meiosis-specific phenotypes in rice (Oryza sativa). In Osrdr6-mei, meiotic double-strand break (DSB) formation is partially blocked.
A research team led by Prof. CHENG Zhukuan at Institute of Genetics and Developmental Biology of Chinese Academy of Sciences created a biallelic mutant with more severe phenotypes, Osrdr6-bi, by crossing Osrdr6-mei with a knockout mutant, Osrdr6-edit. In Osrdr6-bi meiocytes, 24 univalents were observed, and no histone H2AX phosphorylation foci were detected. Compared with the wild type, the number of 21-nucleotide small RNAs in Osrdr6-mei was dramatically lower, while the number of 24-nucleotide small RNAs was significantly higher. Thousands of differentially methylated regions (DMRs) were discovered in Osrdr6-mei, implying that OsRDR6 plays an important role in DNA methylation. There were 457 genes downregulated in Osrdr6-mei, including three genes, CENTRAL REGION COMPONENT1, P31comet, and O. sativa SOLO DANCERS, related to DSB formation. Interestingly, the downregulated genes were associated with a high level of 24-nucleotide small RNAs but less strongly associated with DMRs. Therefore, researchers speculated that the alteration in expression of small RNAs in Osrdr6 mutants leads to the defects in DSB formation during meiosis, which might not be directly dependent on RNA-directed DNA methylation.
The study was published in The Plant Cell on July 30. PhD student LIU Changzhen at University of Chinese Academy of Sciences, associate researcher Dr. SHEN Yi at Institute of Genetics and Developmental Biology of Chinese Academy of Sciences, and Dr. TAN Baoxiang graduated from University of Chinese Academy of Sciences, contributed equally to the study. Prof. CHENG Zhukuan and Prof. WU Yufeng (Nanjing Agricultural University) are the corresponding authors. Prof. CHENG is also a doctoral supervisor at University of Chinese Academy of Sciences. The study was funded by National Natural Science Foundation of China and Strategic Priority Research Program of the Chinese Academy of Sciences.
