Reduced Plasma Membrane H + -ATPase Isoform OsA7 Expression and Proton Pump Activity Decrease Growth Without Affecting Nitrogen Accumulation in Rice

Plasma membrane H + -ATPase (PM H + -ATPase, EC 3.6.1.3.) is a proton pump that is necessary to promote cell growth and ion fluxes across the plasma membrane. The main goal of this study was to evaluate the role of PM H + -ATPase isoform OsA7 expression in rice growth and nitrogen (N) accumulation using three genetically engineered lineages with artificial micro RNA (amiRNA) targeting OsA7 ( osa7.1 , osa7.2, and osa7.3 ). PM H + -ATPase isoform expression in rice shoots and roots (wild-type) revealed that OsA7 is highly expressed in roots and is the most highly expressed PM H + -ATPase isoform. The three osa7 lineages had lower fresh weight, grain yield, height, and 1000-grain weight compared to control IRS plants. The hydroponic experiment comprised three NO 3 − levels over 30 days: 0.2 mM NO 3 − –N, 2.0 mM NO 3 − –N, and NO 3 − starvation for 3 days. The three osa7 lineages had lower PM H + -ATPase and V-H + -PPase activity as compared to the IRS plants. The root and shoot fresh weights were lower in osa7 lineages. The root/shoot ratio was lower in the osa7 lineages cultivated without nitrogen for 3 days and with 0.2 mM of NO 3 − –N as compared to IRS, and did not change in plants cultivated with 2.0 mM NO 3 − –N. The total N concentration did not change in the three osa7 lineages as compared to IRS. Overall, the results indicate that OsA7 is important for rice growth, grain production, and root growth, but does not affect N accumulation, highlighting the importance of other PM H + -ATPase isoforms in N uptake.