Pepper clade A PP2C, CaSIP1, negatively modulates drought resistance by suppressing CaSnRK2.6 kinase activity

Abstract

The phytohormone abscisic acid (ABA) plays a key role in plant response and adaptation to various environmental stimuli, including drought and salinity. As an ABA signaling core component, the serine/threonine kinase SnRK2.6/OST1 is known to undergo post-translational modifications in the modulation of ABA and drought stress responses. However, which proteins are involved in the process remains largely unclear in pepper plants. Here, we tried to isolate CaSnRK2.6-interacting partners through yeast two-hybrid screening and identified the type 2 C protein phosphatase CaSIP1 (Capsicum annuumSnRK2.6-interacting protein phosphatase 1), which belongs to the PP2CA branch. CaSIP1 transcript levels were enhanced by abiotic stress and ABA treatments. Our kinase assays showed that the CaSIP1 protein significantly suppressed the phosphorylation activity of CaSnRK2.6, but its amino acid–substitution mutant did not. Due to PP2C gene redundancy in pepper plants, we alternatively generated CaSIP1-overexpressing (OX) transgenic Arabidopsis plants to understand how CaSIP1 functionally contributes to plant responses to ABA and drought stress. Phenotypic analysis revealed that, compared to wild-type plants, CaSIP1-OX plants were hypersensitive to drought stress and hyposensitive to ABA. Collectively, our findings indicate that CaSIP1 negatively modulates the drought stress response via inhibiting CaSnRK2.6 kinase activity.