The NAF domain defines a novel protein-protein interaction module conserved in Ca2+-regulated kinases

Abstract

The Arabidopsis calcineurin B-like calcium sensor proteins (AtCBLs) interact with a group of serinethreonine protein kinases (AtCIPKs) in a calciumdependent manner. Here we identify a 24 amino acid domain (NAF domain) unique to these kinases as being required and suf®cient for interaction with all known AtCBLs. Mutation of conserved residues either abolished or signi®cantly diminished the af®nity of AtCIPK1 for AtCBL2. Comprehensive two-hybrid screens with various AtCBLs identi®ed 15 CIPKs as potential targets of CBL proteins. Database analyses revealed additional kinases from Arabidopsis and other plant species harbouring the NAF interaction module. Several of these kinases have been implicated in various signalling pathways mediating responses to stress, hormones and environmental cues. Full-length CIPKs show preferential interaction with distinct CBLs in yeast and in vitro assays. Our ®ndings suggest differential interaction af®nity as one of the mechanisms generating the temporal and spatial speci®city of calcium signals within plant cells and that different combinations of CBL±CIPK proteins contribute to the complex network that connects various extracellular signals to de®ned cellular responses.

Dual Fatty Acyl Modification Determines the Localization and Plasma Membrane Targeting of CBL/CIPK Ca2+ Signaling Complexes in Arabidopsis

“…Similarly, overexpression of the vacuolar membrane (tonoplast)-localized CBL2, which, like CBL1, interacts with the kinases CIPK1 and CIPK24 (Albrecht et al, 2001(Albrecht et al, , 2003, did not efficiently complement the cbl1 phenotype (survival rate of 21.7 6 2.9%). This result indicates a rather high functional specificity of the distinct CBL isoform in signal-response coupling.…”

“…Hydrophobic interactions mediate the binding of CBL proteins to the NAF domain of their target kinases, which, because of this specific interaction, have been designated the CBL-interacting protein kinases (CIPKs) (Albrecht et al, 2001;Kolukisaoglu et al, 2004;Sanchez-Barrena et al, 2007).…”

“…In Arabidopsis,10 CBLs that specifically interact with distinct family members of the 25 CIPKs form a network-like signaling system for specific and synergistic stimulus-response coupling (Albrecht et al, 2001;Luan et al, 2002;Batistic and Kudla, 2004). Reverse genetics analyses have uncovered important functions of these proteins in abiotic stress responses and in the regulation of ion homeostasis (Albrecht et al, 2003;Zhu, 2003;Xu et al, 2006).…”

Tonoplast calcium sensors CBL2 and CBL3 control plant growth and ion homeostasis through regulating V-ATPase activity in Arabidopsis

“…These non-catalytic Ca 2+ sensors play crucial roles in Ca 2+ -dependent processes through physically interacting with and activating a group of protein kinases designated as CBL-interacting protein kinases (CIPKs) [12][13][14]. In Arabidopsis, several CBLs coupled with their target CIPKs have been demonstrated to function in response to ionic stress conditions including high sodium (Na + ) and low potassium (K + ) [15].…”

A Ca 2+ signaling pathway regulates a K + channel for low-K response in Arabidopsis

“…Calcineurin B-like (CBL) proteins are a unique family of calcium sensors in plants (14,15). The CBL proteins function by interacting with and regulating a unique family of plant protein kinases (called CIPKs for CBL-interacting protein kinases) (15)(16)(17)(18)(19). The presence of multigene families of CBLs and CIPKs in Arabidopsis suggests that CBL-CIPK network may be involved in a number of signaling processes in plants (20 -22, ‡).…”