Control of female gamete formation by a small RNA pathway in Arabidopsis.

Female gametes in flowering plants develop from a meiotic division of a precursor cell followed by mitotic divisions of one of the resulting haploid cells to yield the gametophyte. Here, ARGONAUTE 9 (AGO9) — a protein involved in RNA interference — is identified as a factor required for specification of the gametophyte. AGO9 is found not in the cell destined to be the gametophyte, but in the neighbouring companion cells, suggesting that it functions in a non-cell-autonomous manner.