The CBL-CIPK signaling module in plants: a mechanistic perspective

In a given environment, plants are constantly exposed to multitudes of stimuli. These stimuli are sensed and transduced to generate a diverse array of responses by several signal transduction pathways. Calcium (Ca2+) signaling is one such important pathway involved in transducing a large number of stimuli or signals in both animals and plants. Ca2+ engages a plethora of decoders to mediate signaling in plants. Among these groups of decoders, the sensor responder complex of calcineurin B-like protein (CBL) and CBL-interacting protein kinases (CIPKs) play a very significant role in transducing these signals. The signal transduction mechanism in most cases is phosphorylation events, but some structural role for the pair has also come to light recently. In this review, we discuss the structural nature of the sensor-responder duo; their mechanism of substrate phosphorylation and also their structural role in modulating targets. Moreover, the mechanism of complex formation and mechanistic role of protein phosphatases with CBL-CIPK module has been mentioned. A comparison of CBL-CIPK with other decoders of Ca2+ signaling in plants also signifies the relatedness and diversity in signaling pathways. Further an attempt has been made to compare this aspect of Ca2+ signaling pathways in different plant species to develop a holistic understanding of conservation of stimulus-response-coupling mediated by this Ca2+-CBL-CIPK module.