Figure 10.

Working model for the essential role of MON1/CCZ1-mediated Rab7 activation in regulating tapetal PCD. Tapetal PCD requires Rab7-mediated vacuolar transport of tapetum degradation-related Cys proteases. Vacuole rupture releases mature Cys proteases, which triggers the PCD in wild-type (WT) tapetum. The cell contents, including the tapetosomes and elaioplasts, then contribute to the formation of pollen coats (A). However, MON1 mutation inhibits vacuolar transport of Cys proteases and their maturation, resulting in delayed tapetal PCD and formation of abnormal pollen coats (B). Ts, Tapetosome; El, elaioplast.