Role of Arabidopsis C2 Domain Calcium-Dependent Protein (AtCLB) in Abiotic Stress Signaling

Plant growth and productivity are greatly affected by abiotic stress factors. Understanding the components and networks of plant stress signal transduction is therefore of fundamental importance and forms an important research topic. Ca²⁺ binding proteins are key players in the transduction of Ca²⁺ signals that are being produced during stress episodes to downstream signaling components. Some of these proteins contain Ca²⁺-dependent, lipid-binding domains or C2 domains. There are a few reports describing involvement of C2 domain proteins in plant responses to abiotic and biotic stresses. Recently, we have identified a new Arabidopsis calcium-dependent, lipid-binding protein (AtCLB) with a C2-like domain that can act as a repressor of abiotic stress response. We found that a disruption in the AtCLB gene locus (At3g61050) can lead to an increased tolerance to salt and drought stress in Arabidopsis loss-of-function mutants. We also clarified the Ca²⁺ and lipid-binding characteristics of the AtCLB protein by demonstrating that AtCLB is able to bind membrane sphingolipid ceramide. By using yeast two-hybrid screen, we were able to identify several other proteins that can interact with AtCLB giving more insights into its molecular function. We further confirmed their physical interactions in-vivo using a mammalian expression system and in-planta using BRET. Based on these findings, a hypothetical model of involvement of AtCLB in plant stress signaling was generated. Furthermore, C2 domain of AtCLB has close homologues in important crops, including tomato and rice and hence our findings can potentially promote novel genetic engineering strategies for improving stress tolerance in these plants.