Multiple roles for small RNAs during plant reproduction

Germline development and early embryogenesis in eukaryotes are characterized by large-scale genome reprogramming events. In companion cells of the Arabidopsis male gametophyte, epigenome reorganization leads to loss of heterochromatin and production of a distinct small RNA (sRNA) population. A specific class of sRNA derived from transposons appears to be mobile and can accumulate in germ cells. In the germline of maize, rice, and Arabidopsis, specific ARGONAUTE–sRNA silencing complexes appear to play key roles in reproductive development, including meiosis and regulation of germ cell fate. These results reveal new roles for sRNAs during plant reproduction and suggest that mobility of sRNAs could be critical for some of these functions.

► Epigenome reprogramming in the vegetative nucleus of pollen grains results in the production of mobile, transposable element (TE)-derived sRNAs, which accumulate in the germline to possibly protect it against movement of TEs.
► In monocots and dicots, AGO-sRNAs complexes play critical roles in meiosis.
► Repression of germ cell fate is dependent on AGO9 in Arabidopsis.
► 24nt sRNAs derived specifically from the maternal genome are produced in the endosperm.