LAUSR

Plasma membrane (PM) H+-ATPase is a pivotal enzyme for plant growth and development that acts as a primary transporter and is activated by phosphorylation of the penultimate residue, threonine, at the C-terminus. Photosynthetically active radiation activates PM H+-ATPase via phosphorylation in mesophyll cells of Arabidopsis thaliana, and phosphorylation of PM H+-ATPase depends on photosynthesis and photosynthesis-related sugar supplementation, such as sucrose, fructose and glucose. However, the molecular mechanism and the physiological role of photosynthesis-dependent PM H+-ATPase activation are still unknown. Analysis using sugar analogues, such as palatinose, turanose, and 2-deoxy glucose, revealed that sucrose metabolites and products of glycolysis such as pyruvate induce phosphorylation of PM H+-ATPase. Transcriptome analysis showed that novel isoform of the Small Auxin Up RNA genes, SAUR30, is upregulated in a light- and sucrose-dependent manner. Time course analyzes of sucrose supplementation showed that phosphorylation level of PM H+-ATPase increased within 10 min, but expression level of SAUR30 increased later than 10 min. The results suggest two temporal regulations may participate in the regulation of PM H+-ATPase. Interestingly, a 15NO3- uptake assay in leaves showed that light increases 15NO3- uptake, and that increment of 15NO3- uptake depends on PM H+-ATPase activity. The results opened the possibility of physiological role of photosynthesis-dependent PM H+-ATPase activation in the uptake of NO3-. We speculate that PM H+-ATPase may connect photosynthesis and nitrogen metabolism in leaves.