Arabidopsis shaker pollen inward K^+ channel SPIK functions in SnRK1 complex-regulated pollen hydration on the stigma

Pollen hydration is a critical step that determines pollen germination on the stigma. KINβγ is a plantspecific subunit of the SNF1-related protein kinase 1 complex(SnRK1 complex). In pollen of the Arabidopsis kinbg mutant, the levels of reactive oxygen species were decreased which lead to compromised hydration of the mutant pollen on the stigma. In this study, we analyzed gene expression in kinβγ mutant pollen by RNA-seq and found the expression of inward shaker K^+ channel SPIK was down-regulated in the kinβγ pollen. Furthermore, we showed that the pollen hydration of the Arabidopsis spik mutant was defective on the wild-type stigma, although the mutant pollen demonstrated normal hydration in vitro.Additionally, the defective hydration of spik mutant pollen could not be rescued by the wild-type pollen on the stigma,indicating that the spik mutation deprived the capability of pollen absorption on the stigma. Our results suggest that the Arabidopsis SnRK1 complex regulates SPIK expression,which functions in determining pollen hydration on the stigma.

Stigma factors regulating self-compatible pollination

Pollination is one of the most important steps during fertilization and sexual reproduction in plants,and numerous cell-cell interaction events occur between the pistil and the pollen grain/tube during this process.The pollen-stigma interaction is a highly selective process which leads to compatible or incompatible pollination.Previous studies in Solanaceae,Papaveraceae,and Brassicaceae provided some important insights into pollen-stigma recognition in self-incompatible systems.In recent years,considerable data have been available regarding pollen-stigma interaction during self-compatible pollination.In this review,we focus on discussing current knowledge on stigma factors that regulate pollen-stigma interaction in self-compatible systems in comparison with self-incompatible systems.

Towards an understanding of plant reproductive isolation:uncovering the species-specific signal for pollen tube guidance

Fertilization produces diploid zygote as the initiation of new diploid organism by fusing two haploid gametes(sperm and egg cell).Different from animals,plants in angiosperms produce immobile sperms in pollen/pollen tube(male gametophyte).Whereas,the egg cell is located in the female gametophyte(embryo sac)that consists of two female gametes(egg and central cells)and accessory cells(synergids and antipodals).Embryo sac is embedded in the ovule of ovary,which is an enlarged basal portion of the pistil.The growth of pollen tube provides a strategy for the immobile sperm approaching the egg cell.After pollination,pollen germinates at the surface of the stigma and produces pollen tube.It grows through the transmitting tract of the style and emerges from it to enter the ovary in response to certain attracting cues from the ovule.