putative 6 trans-membrane nitrate transporter OsNRT1.1b plays a key role in rice under low nitrogen

OsNRT1.1a is a low-affinity nitrate (NO3 ) transportergene. In this study, another mRNA splicing product,OsNRT1.1b, putatively encoding a protein with six transmembranedomains, was identified based on the rice genomicdatabase and bioinformatics analysis. OsNRT1.1a/OsNRT1.1bexpression in Xenopus oocytes showed OsNRT1.1a-expressingoocytes accumulated 15N levels to about half as compared toOsNRT1.1b-expressing oocytes. The electrophysiological recordingof OsNRT1.1b-expressing oocytes treated with0.25mM NO3 confirmed 15N accumulation data. Morefunctional assays were performed to examine the functionof OsNRT1.1b in rice. The expression of both OsNRT1.1a andOsNRT1.1b was abundant in roots and downregulated bynitrogen (N) deficiency. The shoot biomass of transgenic riceplants with OsNRT1.1a or OsNRT1.1b overexpression increasedunder various N supplies under hydroponic conditionscompared to wild-type (WT). The OsNRT1.1a overexpressionlines showed increased plant N accumulation compared tothe WT in 1.25mM NH4NO3 and 2.5mM NO3– or NH4ttreatments, but not in 0.125mMNH4NO3. However, OsNRT1.1boverexpression lines increased total N accumulation in allN treatments, including 0.125mM NH4NO3, suggesting thatunder low N condition, OsNRT1.1b would accumulate more N inplants and improve rice growth, but also that OsNRT1.1a hadno such function in rice plants.(NO3?) transporter gene. In this study, another mRNA splicing product, OsNRT1.1b, putatively encoding a protein with six transmembrane domains, was identified based on the rice genomic database and bioinformatics analysis. OsNRT1.1a/OsNRT1.1b expression in Xenopus oocytes showed OsNRT1.1a-expressing oocytes accumulated 15N levels to about half as compared to OsNRT1.1b-expressing oocytes. The electrophysiological recording of OsNRT1.1b-expressing oocytes treated with 0.25?mM NO3? confirmed 15N accumulation data. More functional assays were performed to examine the function of OsNRT1.1b in rice. The expression of both OsNRT1.1a and OsNRT1.1b was abundant in roots and downregulated by nitrogen (N) deficiency. The shoot biomass of transgenic rice plants with OsNRT1.1a or OsNRT1.1b overexpression increased under various N supplies under hydroponic conditions compared to wild-type (WT). The OsNRT1.1a overexpression lines showed increased plant N accumulation compared to the WT in 1.25?mM NH4NO3 and 2.5?mM NO3– or NH4+ treatments, but not in 0.125?mM NH4NO3. However, OsNRT1.1b overexpression lines increased total N accumulation in all N treatments, including 0.125?mM NH4NO3, suggesting that under low N condition, OsNRT1.1b would accumulate more N in plants and improve rice growth, but also that OsNRT1.1a had no such function in rice plants.