Abstract
Cation/H+ exchanger (CAX) is an active transporter, which transports divalent cations using a H+ gradient. Although the CAX was cloned from yeast, cyanobacteria, Arabidopsis, mung bean, and Zea mays, there is no report about the rice CAX, which is a model plant of monocotyledon.
We identified five CAX from rice, and phylogenetically divided them into two clusters. Gene expression and absolute amounts of mRNA in different organs were analyzed by real-time PCR. OsCAX1a showed high expression in almost all organs. OsCAX1b and OsCAX1c were detected in limited organs and their expression levels were very low. The mRNA levels of OsCAX2 and OsCAX3 varied with the organ. OsCAXs were heterologously expressed in yeast to characterize the ion transport activity. All exchangers, except for OsCAX2, conferred the tolerance to Ca2+. OsCAX1a and OsCAX3 conferred the tolerance to Mn2+. The diversity of expression sites and substrates suggest the broad range function of CAX.
