Oryza sativa RNA-dependent RNA polymerase 6 (OsRDR6) contributes to DSB formation in rice meiosis
RNA-dependent RNA polymerase 6 (RDR6) is a core component of the small RNA biogenesis pathway, but its function in meiosis is unclear. Herein we report a new allele of OsRDR6 (Osrdr6-mei), which causes meiosis-specific phenotype in rice. In Osrdr6-mei, meiotic DSB formation was blocked to some extent. We further created a biallelic mutant, Osrdr6-bi, by crossing Osrdr6-mei with a knock out mutant, Osrdr6-edit (Osrdr6-edi). In Osrdr6-bi, 24 univalents were observed at diakinesis, and no histone H2AX phosphorylation (?H2AX) foci was detected in meiocytes, indicating that OsRDR6 is crucial for meiotic DSB formation. Compared with the wild type, the number of 21-nt small RNAs was dramatically reduced, while the number of 24-nt small RNAs was significantly increased in Osrdr6-mei. And thousands of DMRs discovered in Osrdr6-mei, implying that OsRDR6 plays an essential role on DNA methylation, especially CHH methylation. Meanwhile, the transcriptome data showed that 457 genes were down-regulated in the mutant; including three genes related to DSB formation: OsSDS, P31comet and CRC1. Interestingly, the increased 24-nt small RNA level surrounding down-regulated genes was largely associated with the silencing of these genes, while DMRs were rarely related to them. In summary, we speculated that the small RNA levels are disordered in Osrdr6 mutants, which may lead to the defection of DSB formation. Overall design: We sequenced transcriptome, methylome and small RNA of anthers at the leptotene-like stage between indica rice cultivar Zhongxian 3037 and its mutant.