Figure 6.

A proposed model for ARF10 function in the ovule

(A) In wild-type pre-meiotic ovule nucellus, ARF10 is partially and selectively silenced by STK in both the MMC and nucellus cells. STK binds to the genomic DNA at CArG boxes 1 and 2, repressing ARF10 expression. In the MMC, STK can also induce the expression of miR160 via the RdDM pathway. miR160 subsequently silences ARF10 in collaboration with an AGO protein of unknown identity. In the nucellus cells, AGO1 silences ARF10 in association with an unidentified miRNA. The regulation of ARF10 expression in the funiculus and chalaza regions involves miR160 in conjunction with an unknown AGO protein.

(B) In mARF10 lines, ARF10 is ectopically expressed in the nucellus cells, MMC, and funiculus/chalaza cells. This ectopic expression in the nucellus and MMC results in the widespread commitment of additional cells to form gametophytes. However, only the cell that accumulates meiotic precursors, such as ASY3 (i.e., the MMC), will undergo meiosis (sexual pathway), leading to the formation of a reduced female gametophyte. The generation of additional functional megaspores from somatic companion cells (non-reduced) eventually results in the development of supernumerary, anomalous gametophytes, similar to those observed in aposporous apomictic plants. Black dots represent the cell nuclei, question marks indicate unknown identity.