Abstract
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.