Role of Arabidopsis AtPI4Kγ3, a type II phosphoinositide 4-kinase, in abiotic stress responses and floral transition

Phosphoinositides (PIs) are essential metabolites which are generated by various lipid kinases and rapidly respond to a variety of environmental stimuli in eukaryotes. One of the precursors of important regulatory PIs, phosphatidylinositol (PtdIn) 4-phosphate, is synthesized by PtdIns 4-kinases (PI4K). Despite its wide distribution in eukaryotes, its role in plants remains largely unknown. Here, we show that the activity of AtPI4K gamma 3 gene, an Arabidopsis (Arabidopsis thaliana) type II PtdIn 4-kinase, is regulated by DNA demethylation and some abiotic stresses. AtPI4K gamma 3 is targeted to the nucleus and selectively bounds to a few PtdIns. It possessed autophosphorylation activity but unexpectedly had no detectable lipid kinase activity. Overexpression of AtPI4K gamma 3 revealed enhanced tolerance to high salinity or ABA along with inducible expression of a host of stress-responsive genes and an optimal accumulation of reactive oxygen species. Furthermore, overexpressed AtPI4K gamma 3 augmented the salt tolerance of bzip60 mutants. The ubiquitin-like domain of AtPI4K gamma 3 is demonstrated to be essential for salt stress tolerance. Besides, AtPI4K gamma 3-overexpressed plants showed a late-flowering phenotype, which was caused by the regulation of some flowering pathway integrators. In all, our results indicate that AtPI4K gamma 3 is necessary for reinforcement of plant response to abiotic stresses and delay of the floral transition.