GhCAR4 positively regulates ABA-mediated seed germination, stomatal closure, and drought response as a reciprocal partner of GhCDPK4

Abstract

Drought severely affects cotton growth and yield. The C2 structural domain ABA-associated (CAR) proteins perform important functions in ABA signaling and abiotic stress. In this work, we detected the expression levels of GhCAR4 in response to natural drought conditions simulated using PEG and exogenous ABA treatments. Y2H and BiFC assays confirmed that GhCAR4 interacts with the calcium-sensing GhCDPK4. In GhCDPK4-silenced plants with significantly reduced GhCDPK4 expression levels, the expression level of GhCAR4 was severely downregulated, and ABA pathway core genes were also severely affected. Heterologous overexpression of GhCAR4 enhances growth potential, drought resistance in Arabidopsis thaliana, and antioxidant enzyme activities. In contrast, virus-induced silencing of GhCAR4 reduced drought tolerance and total antioxidant capacity (T-AOC) in cotton. Seed germination was significantly decreased in ABA-treated GhCAR4 over-expressing plants, while stomatal closure was affected in ABA-treated GhCAR4-silenced plants. All the above results prove that GhCAR4, as an interacting protein of GhCDPK4, plays a positive role in ABA-mediated seed germination, stomatal closure, and drought response.