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

Abstract

SUMMARYStimulus-specific calcium (Ca 2+ ) signals have crucial functions 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 (CBL) protein calcium sensors and CBL-interacting protein kinases (CIPKs) has been shown to fulfil 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 remains largely unknown. In this study, we analyzed single and double mutants of the closely related tonoplast-localized calcium sensors CBL2 and CBL3, which show 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, but accumulation of sucrose was not altered. Moreover, accumulation of inositol hexakisphosphate (InsP 6 ), 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 reveal a crucial function of Ca 2+ -controlled processes at the vacuolar membrane as determinants of seed yield and size, and demonstrate the importance of vacuolar CBL calcium sensors for plant embryogenesis.

Calcineurin B-like 3 calcium sensor associates with and inhibits 5′-methylthioadenosine nucleosidase 2 in Arabidopsis

“…Extensive studies from various independent research groups indicated that the CBL family members target only a group of serine/threonine protein kinases called CIPKs [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36]. Until recently, therefore, it had been strongly believed that CBLs do not possess the target diversity exhibited by other sensor relays, CaMs and CMLs.…”

N‐terminal S‐acylation facilitates tonoplast targeting of the calcium sensor CBL6

“…More recent work has uncovered that four of the ten CBLs are localized at the tonoplast membrane [17], and reverse genetic analyses of the calcium sensors CBL2 and CBL3 mutants have uncovered their function in regulating cellular ion homeostasis and their essential role for Arabidopsis pollen, seed and early embryonal development [18][19][20]. Subsequent studies of CIPK quadruple mutants identified CIPK3/ 9/23/26 as the CBL2/3 interacting kinases functioning in regulating cellular magnesium homeostasis [21,22].…”

Calcineurin B-Like Protein-Interacting Protein Kinase CIPK21 Regulates Osmotic and Salt Stress Responses in Arabidopsis

“…(Arabidopsis thaliana) mutants (Zhu, 2002;Cheong et al, 2003Cheong et al, , 2007Kim et al, 2003;Pandey et al, 2004D'Angelo et al, 2006;Qin et al, 2008;Tripathi et al, 2009;Held et al, 2011;Tang et al, 2012;Drerup et al, 2013;Eckert et al, 2014). A few CIPKs have also been functionally characterized by gain-of-function approach in crop plants such as rice (Oryza sativa), pea (Pisum sativum), and maize (Zea mays) and were found to be involved in osmotic stress responses (Mahajan et al, 2006;Xiang et al, 2007;Yang et al, 2008;Tripathi et al, 2009;Zhao et al, 2009;Cuéllar et al, 2010).…”