Over-Expression ofOshox4Enhances Drought and Salinity Tolerance in Rice

Plant hormones play major roles in abiotic stress. This study shows that gibberellin acid-inefficient transgenic rice (Oryza sativaL.) 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 geneOshox4(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 riceOshox4gene for drought and salinity stress tolerance. Phenotypic analysis indicated thatOshox4transgenic lines are more tolerant to drought and salinity stress relative to non-transgenic IR64 plants. To explain the strong osmotic stress tolerance ofOshox4transgenic lines, we studied the expression of rice GA 2-oxidase, rice YABBY, rice KRP, and rice GRAS gene families. qRT-PCR results showed thatOsGA2ox4,OsGA2ox6,OsGA2ox8,OsGAIandOsSCRLwere highly expressed under severe drought inOshox4transgenic plants.Oshox4enhanced the expression ofOsGA2ox5,OsKRP2andOsKRP5under 50 mM salt treatment andOsSCRLunder 200 mM salt treatment. Our findings have confirmed thatOshox4transgenic rice plants are more tolerant to drought and salinity stress and thatOshox4plays 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.