NIMA-related kinases redundantly regulate vegetative and reproductive development in <i>Arabidopsis thaliana</i>

NIMA-related kinases (NEKs) are conserved protein kinases in eukaryotes that regulate cell division and elongation. In Arabidopsis thaliana, NEK6 has been shown to control anisotropic growth through cortical microtubule depolymerization, but the functions of other NEK family members remain largely unknown. Here, we show that Arabidopsis NEKs redundantly regulate organ growth and flowering through phosphorylation-dependent mechanisms. Expression analyses revealed overlapping promoter activities of NEK genes in meristems, vascular tissues, and floral organs. While most single mutants showed no obvious phenotype, multiple mutants exhibited defects in root growth direction, leaf elongation, vascular formation, and floral transition. Biochemical analysis showed that NEK3 and NEK6 phosphorylate both β-tubulin and γ-tubulin, indicating a conserved role in microtubule regulation. In addition, several NEKs interacted with the florigen FLOWERING LOCUS T (FT), and NEK3 phosphorylated FT in vitro and inhibited FT-FD interaction in transient assays, suggesting a role in flowering regulation. These findings show that Arabidopsis NEKs redundantly coordinate vegetative and reproductive development through phosphorylation-dependent regulation of microtubules and flowering pathway.