Abstract
Cation/H+ exchanger (CAX) is an active transporter, which transports divalent cations using a H+ gradient. Previously, we cloned CAX from rice, OsCAX1a, and demonstrated its Ca2+/H+ exchange activity in yeast. The present study aims to elucidate the physiological function of OsCAX1a. First, we examined the response of OsCAX1a to several ions at mRNA and protein levels. Levels of mRNA and protein of OsCAX1a were increased by Ca2+. Second, subcellular localization was determined by expressing GFP-OsCAX1a. Green fluorescence was observed in vacuolar membranes in transiently expressed onion cells. OsCAX1a was immunochemically detected in vacuolar membranes by subcellular fractionation. Third, promoter-GUS analysis revealed that OsCAX1a was expressed in vascular bundles, stomal cells, trichomes, steles, flowers, embryo, and aleurone layers. These results suggest that OsCAX1a transports excess Ca2+ into vacuoles in rice cells, which suffer high Ca2+ concentrations, and is involved in Ca2+ homeostasis in various tissues.
