Calcium Pumps and Interacting BON1 Protein Modulate Calcium Signature, Stomatal Closure, and Plant Immunity

Abstract

Calcium signaling is essential for environmental responses including immune responses. Here, we provide evidence that the evolutionarily conserved protein BONZAI1 (BON1) functions together with autoinhibited calcium ATPase10 (ACA10) and ACA8 to regulate calcium signals in Arabidopsis. BON1 is a plasma membrane localized protein that negatively regulates the expression of immune receptor genes and positively regulates stomatal closure. We found that BON1 interacts with the autoinhibitory domains of ACA10 and ACA8, and the <i>aca10</i> loss-of-function (LOF) mutants have an autoimmune phenotype similar to that of the <i>bon1</i> LOF mutants. Genetic evidences indicate that BON1 positively regulates the activities of ACA10 and ACA8. Consistent with this idea, the steady level of calcium concentration is increased in both <i>aca10</i> and <i>bon1</i> mutants. Most strikingly, cytosolic calcium oscillation imposed by external calcium treatment was altered in <i>aca10</i>, <i>aca8</i>, and <i>bon1</i> mutants in guard cells. In addition, calcium- and pathogen-induced stomatal closure was compromised in the <i>aca10</i> and <i>bon1</i> mutants. Taken together, this study indicates that ACA10/8 and BON1 physically interact on plasma membrane and function in the generation of cytosol calcium signatures that are critical for stomatal movement and impact plant immunity.