Cloning and characterization of CBL-CIPK signalling components from a legume (Pisum sativum)

The studies on calcium sensor calcineurin B-like protein (CBL) and CBL interacting protein kinases (CIPK) are limited to Arabidopsis and rice and their functional role is only beginning to emerge. Here, we present cloning and characterization of a protein kinase (PsCIPK) from a legume, pea, with novel properties. The PsCIPK gene is intronless and encodes a protein that showed partial homology to the members of CIPK family. The recombinant PsCIPK protein was autophosphorylated at Thr residue(s). Immunoprecipitation and yeast two-hybrid analysis showed direct interaction of PsCIPK with PsCBL, whose cDNA and genomic DNA were also cloned in this study. PsCBL showed homology to AtCBL3 and contained calcium-binding activity. We demonstrate for the first time that PsCBL is phosphorylated at its Thr residue(s) by PsCIPK. Immunofluorescence/confocal microscopy showed that PsCBL is exclusively localized in the cytosol, whereas PsCIPK is localized in the cytosol and the outer membrane. The exposure of plants to NaCl, cold and wounding co-ordinately upregulated the expression of PsCBL and PsCIPK genes. The transcript levels of both genes were also coordinately stimulated in response to calcium and salicylic acid. However, drought and abscisic acid had no effect on the expression of these genes. These studies show the ubiquitous presence of CBL/CIPK in higher plants and enhance our understanding of their role in abiotic and biotic stress signalling.