Plants possess sophisticated regulatory mechanisms to balance growth and stress responses. Cyclin-dependent kinases (CDKs) are established regulators of cell division and endoreduplication, yet their roles in abiotic stress responses remain poorly understood.

Here, using reverse genetics, biochemical, and cell biological approaches, we show that Arabidopsis (Arabidopsis thaliana) CDKB1s contribute to salt stress adaptation through a mechanism involving the phosphorylation of MAP65-1 and MAP65-2, two microtubule-associated proteins essential for cytoskeleton dynamics under salt stress.

Loss of CDKB1 function enhances salt tolerance, accompanied by attenuated plasma membrane depolarization and reactive oxygen species accumulation. In vitro phosphorylation assays demonstrate that CDKB1;1 directly phosphorylates MAP65-1 at Ser-503. Genetic analyses indicate that phospho-dead MAP65 variants confer enhanced salt tolerance, whereas phosphomimetic variants compromise tolerance even in the cdkb1;1 1;2 background, supporting a critical role for MAP65 phosphorylation status at these sites in salt stress adaptation. We further found that CDKA;1 can similarly interact with and phosphorylate MAP65-1, suggesting a potential parallel role for CDKA;1 in this process.

Collectively, our findings identify a regulatory module involving CDKs, MAP65, and microtubules that links cell cycle kinases and cytoskeleton dynamics with plant salt stress adaptation.