Two Calcium Sensor-Activated Kinases Function in Root Hair Growth

This study identified CIPK13 and CIPK18 as genes specifically expressed in Arabidopsis root hairs, with double mutants showing reduced root hair length and growth rates. Calcium oscillations at the root hair tip were attenuated in these mutants compared to wild-type plants. Yeast two-hybrid screens revealed that CBL2 and CBL3 interact with CIPK13 and CIPK18, and mutants of cbl2 cbl3 displayed similar shortened root hair phenotypes. Biochemical assays confirmed the activation of CIPK13/18 by CBL2/3, suggesting that CBL2/3 and CIPK13/18 function as Ca2+-decoding modules in controlling root hair growth. This illustrates a molecular mechanism where the same CBLs recruit distinct CIPKs to regulate polarized tip growth in different plant cells.