The Transcription Factor Gene RDD3 Improves Ammonium and Magnesium Uptake and Accumulation and Drought Tolerance in Rice

Abstract

We investigated the expression and functions of a transcription factor gene, RDD3. It displays sequence similarity to RDD1, which controls various nutrient ion accumulation and uptake in rice. The RDD3 protein was specifically localized to protoxylems and metaxylems in the vascular bundles. RDD3-overexpressing (RDD3-OX) plants increased the RDD3 protein levels early in the light period and improved NH₄⁺ and Mg²⁺ uptake and accumulation in the shoots. Furthermore, photosynthetic CO₂ assimilation and stomatal conductance in RDD3-OX plants were higher than in wild-type plants, although shoot dry weight was decreased in mature RDD3-OX plants. Subsequent microarray analysis indicated that the late embryogenesis abundant (LEA) protein genes associated with drought responses were upregulated in RDD3-OX plants, whereas WRKY transcription factor genes were downregulated despite participating in defenses against biotic and abiotic stresses. Examining drought stress tolerance indicated that RDD3-OX plants were more tolerant than wild-type plants. These results indicate that increased RDD3 protein levels early in the light period improve nitrogen and magnesium accumulation and drought stress tolerance in RDD3-OX plants.