CBL-interacting protein kinase 6 (CIPK6) negatively regulates the PAMP-triggered and effector-triggered immune response in Arabidopsis.

Calcium ion (Ca2+) is a ubiquitous second messenger that transmits various internal and external signals including stresses and, therefore, is important for plants’ response process. Calcineurin B-like proteins (CBLs) are one of the plant calcium sensors, which sense and convey the changes in cytosolic Ca2+-concentration for response process. A search in four leguminous plant (soybean, Medicago truncatula, common bean and chickpea) genomes identified 9 to 15 genes in each species that encode CBL proteins. Sequence analyses of CBL peptides and coding sequences (CDS) suggested that there are nine original CBL genes in these legumes and some of them were multiplied during whole genome or local gene duplication. Coding sequences of chickpea CBL genes (CaCBL) were cloned from their cDNAs and sequenced, and their annotations in the genome assemblies were corrected accordingly. Analyses of protein sequences and gene structures of CBL family in plant kingdom indicated its diverse origin but showed a remarkable conservation in overall protein structure with appearance of complex gene structure in the course of evolution. Expression of CaCBL genes in different tissues and in response to different stress and hormone treatment were studied. Most of the CaCBL genes exhibited high expression in flowers. Expression profile of CaCBL genes in response to different abiotic stresses and hormones related to development and stresses (ABA, auxin, cytokinin, SA and JA) at different time intervals suggests their diverse roles in development and plant defence in addition to abiotic stress tolerance. These data not only contribute to a better understanding of the complex regulation of chickpea CBL gene family, but also provide valuable information for further research in chickpea functional genomics.

Calcium is an essential macronutrient and a second messenger for signal transduction in plants. Apart from acting as a second messenger, calcium is also required for cytoskeleton, cell division, pollen tube growth and as a co-factor. Cytoplasmic calcium ion ([Ca 2+ ] cyt) is maintained at a low level, however, is rapidly elevated using storages in organelles on perception of a stimulus. Ca 2+-binding proteins that sense the kinetics and magnitude of elevated [Ca 2+ ] cyt convert the chemical signals to biological signals and define specificity of responses. These proteins are broadly classified into sensor relays and sensor responders. Sensor relay proteins require another interacting protein to transmit the signal; whereas, the sensor responders combine within one protein the relay, amplification and response functions. A significant achievement has been made in the last three decades that identified and characterized various proteins instrumental in decoding Ca 2+-signals in plant cells. The latest addition in Ca 2+-signaling is Calcineurin B-like proteins (CBLs) and their interacting kinases (CIPKs). It is believed that flexibility of interactions between different CBL and CIPK proteins and their sub-cellular localizations are crucial in sensing and responding to specific signals. In this review, we have laid emphasis on the recent and emerging advancements in understanding of the CBL-CIPK module.

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