Experimental Farm • Nonomura Group Plant Genetics Laboratory • Kurata Group

Meiosis is a pivotal biological event for breeding programs, and elucidatiing molecular mechanisms of meiosis will lead to achieve stable and efficient seed production. In this paper, we focus on MEL1 protein, which plays essential roles in progression of meiosis in rice. MEL1 is an Argonaute family protein known as an effecter of RNA silencing.

Of all MEL1-binding small RNAs (MEL1-sRNA) isolated and sequenced, 75% were 21 nt long and 80% beared a 5′-terminal cytosine. Supprisingly, MEL1-sRNA derived from more than 1,000 genomic loci, and most of the loci were mapped onto the intergenic regions. We discovered that more than 700 species of large intergenic noncoding RNAs (lincRNA) were transcribed from the MEL1-sRNA loci after the reproductive phase transition. The lincRNAs were double-stranded and processed in the 21-nt phase by tasiRNA biogenesis pathway, resulting in production of the 21-nt small RNAs including MEL1-sRNA.

This study brought us important information to consider the role of RNA silencing in plant germline development and meiosis.

Analysis of MEL1, the rice Argonaute protein with specific expression in the germline.
(A) The mel1 mutant is sterile. (B) MEL1 gene is expressed in germ cells. (C) RNA-immunoprecipitation of wt (1) and muntat panicles (2). (D) MEL1-binding small RNAs derive from >1,000 intergenic loci (blue). (E) ZEP1 doesn’t elongate between homolog pairs in mel1 meiocytes.
Panels A-B and C-E were cited from Plant Cell 19: 2583-2594 (2007) and Plant J (2014), respectively, with slight modifications.