The cysteine-rich receptor-like kinase CRK4 contributes to the different drought stress response between Columbia and Landsberg erecta.

The natural variation between Arabidopsis (Arabidopsis thaliana) ecotypes Columbia (Col) and Landsberg erecta (Ler) strongly affects abscisic acid (ABA) signalling and drought tolerance. Here, we report that the cysteine-rich receptor-like protein kinase CRK4 is involved in regulating ABA signalling, which contributes to the differences in drought stress tolerance between Col-0 and Ler-0. Loss-of-function crk4 mutants in the Col-0 background were less drought tolerant than Col-0, whereas overexpressing CRK4 in the Ler-0 background partially to completely restored the drought-sensitive phenotype of Ler-0. F1 plants derived from a cross between the crk4 mutant and Ler-0 showed an ABA-insensitive phenotype with respect to stomatal movement, along with reduced drought tolerance like Ler-0. We demonstrate that CRK4 interacts with the U-box E3 ligase PUB13 and enhances its abundance, thus promoting the degradation of ABA-INSENSITIVE 1 (ABI1), a negative regulator of ABA signalling. Together, these findings reveal an important regulatory mechanism for modulating ABI1 levels by the CRK4-PUB13 module to fine-tune drought tolerance in Arabidopsis.