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 plant-specific subunit of the SNF1-related protein kinase 1 complex (SnRK1 complex). In pollen of the Arabidopsis kinβγ 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.