image: Spatial distribution and biogenesis of two types phasiRNAs. miR2118 specifically accumulates in anther wall cells, where 21-nt phasiRNA are produced. By contrast, 24-nt phasiRNA biogenesis occurs mainly in meiocytes, where miR2275 and OsAGO1d accumulate. During phasiRNA biogenesis, OsAGO1d binds miR2118 and miR2275 to form RNA-induced silencing complexes that mediate the initial cleavage of long non-coding precursor RNAs. The cleavageproducts are converted into double-stranded RNAs by RDR6 and further diced into 21- and 24-nt phasiRNAs by DCL4 and DCL3b/DCL5, respectively. 21-nt phasiRNAs with 5′U and 5′C can be loaded into OsAGO1d and MEL1 for execution. 24-nt phasiRNAs could be loaded into currently unknown AGO proteins and may mediate DNA methylation of target sites. Upon cold treatment, OsAGO1d is induced and required to sustain male fertility, as WT plants produce viable pollen but osago1d mutants produce inviable pollen. view more
Credit: ©Science China Press
This study is led by Dr. Xiaofeng Cao, and Dr. Xianwei Song (Institute of Genetics and Developmental Biology, Chinese Academy of Sciences). Grass anthers produce abundant phased small interfering RNAs (phasiRNAs) with sizes of 21- and 24-nt, which regulate male fertility similar to piRNAs in animals. PhasiRNA biogenesis requires 22-nt miR2118 and miR2275 loading into AGO protein to mediate the initiation of cleavage of PHAS transcripts, which are subsequently processed by RDR6 and DCLs to produce mature phasiRNAs (Johnson et al., 2009; Song et al., 2012a; Song et al., 2012b; Teng et al., 2020). The rice AGO5 family member MEIOSIS ARRESTED AT LEPTOTENE 1 (MEL1) binds 21-nt phasiRNAs with a 5′ terminal C to regulate meiosis in rice (Nonomura et al., 2007; Komiya et al., 2014); however, whether there are other phasiRNA-associated AGOs remains unknown.
The research team found that OsAGO1d was induced by low-temperature in rice. Loss of OsAGO1d function causes low-temperature male sterility associated with delayed programmed cell death of tapetal cells during anther development. Researchers performed immunoprecipitation and analyzed small RNAs bound by OsAGO1d. It was found that 22-nt miRNAs and 21-nt phasiRNAs with 5’U were mainly associated with OsAGO1d. These 22-nt miRNAs are mainly miR2118 and miR2275 family members. Genome-wide small RNA sequencing revealed that OsAGO1d mediated phasiRNA production from nearly a thousand PHAS loci.It is interesting that the transcripts of OsAGO1d were mainly expressed in anther wall cells, whereas proteins were located in meiocytes. This suggests that OsAGO1d protein can move from anther wall cells to meiocytes. The role for OsAGO1d movement is to load miRNA2275 producing 24-nt phasiRNAs which are mainly in meiocytes. This study demonstrates the essential role of OsAGO1d mediating phasiRNA biogenesis in male fertility at low temperature. The mobility of OsAGO1d regulates spatiotemporal distribution of phasiRNAs, which provide a new signal communication between anther wall cells and meiocytes during anther development.
See the article:
Mobile ARGONAUTE 1d binds 22-nt miRNAs to generate phasiRNAs important for low-temperature male fertility in rice
https://doi.org/10.1007/s11427-022-2204-y
Journal
Science China Life Sciences