SCaBP3/CBL7 negatively regulates the plasma membrane H+-ATPase and modulates hypocotyl elongation in Arabidopsis

The regulation of hypocotyl elongation is an important process in plant growth and development and depends on the activity of the plasma membrane (PM) H+-ATPase. In this study, we found that the Arabidopsis protein SOS3-LIKE CALCIUM BINDING PROTEIN3 (SCaBP3) negatively regulates PM H+-ATPase activity in yeast and hypocotyl elongation in dark-grown seedlings. Yeast two-hybrid assays showed that SCaBP3 interacts with representative members of the Arabidopsis PM H+-ATPase family. Experiments in RS-72 yeast showed that SCaBP3 negatively regulates PM H+-ATPase activity-dependent yeast cell growth. Hypocotyl elongation was promoted in the loss-of-function mutant scabp3 and inhibited in SCaBP3 overexpression lines of Arabidopsis. We propose that SCaBP3 modulates hypocotyl elongation by negatively regulating PM H+-ATPase activity.