Binding of 14-3-3κ to ADF4 is involved in the regulation of hypocotyl growth and response to osmotic stress in Arabidopsis

14-3-3 proteins, a family of conserved molecules in eukaryotes, target a number of protein clients through their ability to recognize well-defined phosphorylated motifs. ADF4, as one of Actin-Depolymerizing Factor (ADF) family of proteins, is involved in plant development, and response to biotic and abiotic stresses. Here, we show that 14-3-3 kappa specially interacted with ADF4 in vitro and in vivo. The 14-3-3 kappa xadf4 double mutant displayed less F-actin bundle and shorter hypocotyl compared with adf4 mutant, indicating that 14-3-3 kappa acts upstream of ADF4 to mediate the hypocotyl growth in the dark-grown seedlings. Under the osmotic stress, 14-3-3 kappa mutants displayed less survival rate than wild-type plants. The adf4 mutants exhibited markedly enhanced survival rate under osmotic treatment, while ADF4-overexpressing plants displayed the opposite results, indicating that ADF4 plays a negative role in response to osmotic stress in Arabidopsis. The interaction between ADF4 and 14-3-3 kappa inhibited the association of ADF4 with actin filament. Moreover, the in vitro phosphorylation assay demonstrates that the phosphorylation of ADF4 by CASEIN KINASE1-LIKE PROTEIN2 (CKL2) was enhanced by binding 14-3-3 kappa. Collectively, our data infer a fundamental role for the interaction between 14-3-3 kappa and ADF4 in regulating hypocotyl growth and osmotic tolerance of plants.

Automated summary

The study reveals the specific interaction between 14-3-3 kappa and ADF4, which is involved in plant growth and response to stress. ADF4 plays a negative regulatory role in osmotic stress response, and its association with actin filaments is inhibited by binding with 14-3-3 kappa. These findings highlight the importance of the interaction between 14-3-3 kappa and ADF4 in regulating plant growth and tolerance.