The vacuolar calcium sensors CBL2 and CBL3 affect seed size and embryonic development in Arabidopsis thaliana.

Eckert C, Offenborn JN, Heinz T, Armarego-Marriott T, Schültke S, Zhang C, Hillmer S, Heilmann M, Schumacher K, Bock R, Heilmann I, Kudla J

Abstract

Stimulus-specific calcium (Ca(2+) ) signals crucially function in developmental processes in many organisms and are deciphered by various Ca(2+) binding proteins. In Arabidopsis thaliana, a signaling network consisting of Calcineurin B-like protein (CBL) calcium sensors and CBL-interacting protein kinases (CIPKs) has been shown to fulfill pivotal functions at the plasma membrane in regulating ion fluxes and abiotic stress responses. However, the role of tonoplast localized CBL proteins and especially their function in regulating developmental programs has remained largely unknown. In this study we analyzed single and double mutants of the closely-related tonoplast localized calcium sensors CBL2 and CBL3 with either reduction of function (rf) or complete loss of function (lf). While single cbl2 or cbl3 mutants did not display discernable phenotypes, cbl2/cbl3 mutants exhibited defects in vegetative growth and were severely impaired in seed development and morphology. Seeds of the cbl2/3rf mutant were smaller in size and exhibited reduced weight and fatty acid content compared to wild type while accumulation of sucrose was not altered. Moreover, accumulation of inositol hexakisphosphate (InsP6 ), the major storage form of phosphorus in seeds, was significantly reduced in mutant seeds. In addition, complete loss of CBL2 and CBL3 function in cbl2/3lf resulted in a high frequency of severe defects in embryonic development. Together our findings uncover a crucial function of Ca(2+) controlled processes at the vacuolar membrane as determinants of seed yield and size and reveal the importance of vacuolar CBL calcium sensors for plant embryogenesis. This article is protected by copyright. All rights reserved.