Expression of the plasma membrane H+-ATPase gene in response to salt stress in a rice salt-tolerant mutant and its original variety

Plasma membrane (PM) H+-ATPase plays an important role in the establishment and maintenance of ion homeostasis. To investigate its expression in the rice salt-tolerant mutant M-20 and the original variety 77-170 during salt stress, a cDNA fragment corresponding to the PM H+-ATPase gene was obtained by PCR from rice japonica variety 77-170 and designated as OSA3. Sequence analysis of OSA3 revealed its high homology with two other published PM H+-ATPase genes, OSA1 and OSA2, in rice. Southern-blot analysis detected a RFLP between M-20 and 77-170, and one copy of the OSA3 gene was mapped to a position on rice chromosome 12 where a salt tolerance QTL was closely located. The expression of the PM H+-ATPase gene, as revealed by the OSA3 fragment, was compared between M-20 and 77-170. The results demonstrated that M-20 shoots accumulated less transcripts than 77-170 shoots at a later stage of salt treatment, and M-20 showed high expression at 300 mM NaCl while 77-170 reached its maximum at 200 mM NaCl. In roots, the difference in the level of the PM H+-ATPase gene expression between stressed and non-stressed plants was substantially greater in M-20 than that in 77-170. The relative abundance of PM H+-ATPase gene transcripts in M-20 roots may indicate the active role of this gene in the strict control of Na+ and Cl+ uptake into root symplast and apoplast, and further translocation into the shoot, hence leading to the reduced gene expression of M-20 shoots under salt-stress conditions.