Two pepper subclass II SnRK2 genes positively regulate drought stress response, with differential responsiveness to abscisic acid.

Abstract

Sucrose nonfermenting-1-related protein kinase 2 (SnRK2) intricately modulates plant responses to abiotic stresses and abscisic acid (ABA) signaling. In pepper genome, five SnRK2 genes with sequence homology to CaSnRK2.6 showed distinct expression patterns across various pepper organs and in response to treatments with ABA, drought, mannitol, and salt. This study elucidated the roles of two pepper (Capsicum annuum) subclass II SnRK2s-CaDSK2-1 and CaDSK2-2-in ABA signaling and stress responses. ABA specifically induced CaDSK2-1 activity, whereas CaDSK2-2 did not respond to ABA. Both kinases displayed stress-induced kinase activity, with CaDSK2-2 showing faster and stronger activation in response to drought and mannitol than that of CaDSK2-1. Unlike CaDSK2-2, CaDSK2-1 overexpression in pepper plants led to increased leaf temperatures and enhanced ABA-responsive gene expression in response to ABA treatment compared with those of the control. However, both kinases contributed to enhanced drought resistance. During seed germination in Arabidopsis, the overexpression of CaDSK2-2, but not CaDSK2-1, led to ABA hypersensitivity. Among the key regulators of the ABA signaling pathway, CaDSK2-1 specifically interacts with clade A protein phosphatase 2C (PP2C) CaADIP1, whereas CaDSK2-2 interacts with various PP2Cs, including CaADIP1. CaADIP1 negatively regulated the kinase activity of both CaDSK2-1 and CaDSK2-2 and mitigated ABA hypersensitivity mediated by CaDSK2-2 during Arabidopsis seed germination. These findings suggest distinct roles for pepper subclass II SnRK2s in drought stress responses and ABA signaling.