Boron deficiency increases the levels of cytosolic Ca2+ and expression of Ca2+-related genes in Arabidopsis thaliana roots

Abstract

Boron (B) deficiency affects the expressions of genes involved in major physiological processes. However, signal transduction pathway through which plants are able to sense and transmit B-deprivation signal to the nucleus is unknown. The aim of this work was to research in Arabidopsis thaliana roots whether the short-term B deficiency affects cytosolic Ca(2+) levels ([Ca(2+)]cyt) as well as expression of genes involved in Ca(2+) signaling. To visualize invivo changes in root [Ca(2+)]cyt, Arabidopsis seedlings expressing Yellow Cameleon (YC) 3.6 were grown in a nutrient solution supplemented with 2μM B and then transferred to a B-free medium for 24h. Root [Ca(2+)]cyt was clearly higher in B-deficient seedlings upon 6 and 24h of B treatments when compared to controls. Transcriptome analyses showed that transcript levels of Ca(2+) signaling-related genes were affected by B deprivation. Interestingly, Ca(2+) channel (CNGC19, cyclic nucleotide-gated ion channel) gene was strongly upregulated as early as 6h after B deficiency. Expression levels of Ca(2+) transporter (ACA, autoinhibited Ca(2+)-ATPase; CAX, cation exchanger) genes increased when seedlings were subjected to B deficiency. Gene expressions of calmodulin-like proteins (CMLs) and Ca(2+)-dependent protein kinases (CPKs) were also overexpressed upon exposure to B starvation. Our results suggest that B deficiency causes early responses in the expression of CNGC19 Ca(2+)-influx channel, ACA- and CAX-efflux, and Ca(2+) sensor genes to regulate Ca(2+) homeostasis. It is the first time that changes in the levels of invivo cytosolic Ca(2+) and expression of Ca(2+) channel/transporter genes are related with short-term B deficiency in Arabidopsis roots.