In Brassicaceae, self-incompatibility is initiated when the pollen ligand SP11/SCR activates the cognate stigma receptor kinase SRK. Although this interaction is usually considered at a single pollen-papilla interface, individual papilla cells encounter mixed pollen loads. Here, using a self-incompatibility-reconstituted Arabidopsis thaliana system, we show that self-pollen recognition transiently delays the hydration and germination of neighboring nonself pollen. The delay was stronger when two self-pollen grains were present but largely disappeared when nonself pollen was applied 2 h after self pollen. Repollination after removal of a self-pollen grain nevertheless revealed persistent inhibition at the original contact site. Live imaging with Lifeact-tdTomato showed that self-pollination transiently broadened F-actin orientations throughout the papilla cell, followed by recovery toward the longitudinal organization of unpollinated cells. Upon self- and non-self-dual pollination, actin-bundle orientation returned toward the papilla long axis prior to the delayed hydration of the non-self-pollen. These observations support the view that the nature of the self-recognition signaling produces a reversible, papilla-wide state that temporarily reduces compatible-pollen acceptance, while local self-rejection persists at the original contact site.
Inoue, Y., Fujii, S.
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