Over-Expression of Oshox4 Enhances Drought and Salinity Tolerance in Rice

Plant hormones play major roles in abiotic stress. This study shows that gibberellin acid-inefficient transgenic rice (Oryza sativa L.) is more tolerant to drought and salinity stress. We also investigated the underlying molecular mechanism by which plants respond to salinity and drought stress. We previously showed how the HD-Zip family I gene Oshox4 (Homeobox 4) regulates GA deactivation by controlling DELLA subfamily and rice GA 2-oxidase and GA 3-oxidase genes in rice. Here we investigated the role of rice Oshox4 gene for drought and salinity stress tolerance. Phenotypic analysis indicated that Oshox4 transgenic lines are more tolerant to drought and salinity stress relative to non-transgenic IR64 plants. To explain the strong osmotic stress tolerance of Oshox4 transgenic lines, we studied the expression of rice GA 2-oxidase, rice YABBY, rice KRP, and rice GRAS gene families. qRT-PCR results showed that OsGA2ox4, OsGA2ox6, OsGA2ox8, OsGAI and OsSCRL were highly expressed under severe drought in Oshox4 transgenic plants. Oshox4 enhanced the expression of OsGA2ox5, OsKRP2 and OsKRP5 under 50 mM salt treatment and OsSCRL under 200 mM salt treatment. Our findings have confirmed that Oshox4 transgenic rice plants are more tolerant to drought and salinity stress and that Oshox4 plays a role in rice osmatic tolerance. This study provides novel insights into methods of maintaining higher yield amidst a limited supply of water by improving physiological conditions.