ABSTRACT: To discover new mutants conferring enhanced tolerance to drought stress, we screened a mutagenized rice (O. sativa) population (cv. IAPAR9) and identified a mutant, named idr1-1 (for increased drought resistance 1-1), with obviously increased drought tolerance under upland field conditions. The idr1-1 mutant possessed a significantly enhanced ability to tolerate high-drought stresses. Map-based cloning revealed that the gene LOC_Os05g26890 (corresponding to D1 or RGA1 gene), residing in the mapping region of IDR1 locus, carried a single-base deletion in idr1-1 mutant. IDR1 protein was localized in nucleus and to plasma membrane or cell periphery. Further investigations indicated that the significantly increased drought tolerance in idr1-1 mutant stemmed from a range of physiological and morphological changes, including greater leaf potentials, increased proline contents, heightened leaf thickness, and upregulation of antioxidant-synthesizing and drought-induced genes, etc., under drought-stressed conditions. Especially, ROS production might be remarkably impaired, while ROS-scavenging ability appeared to be markedly enhanced as a result of significantly elevated expression of ROS-scavenging enzyme genes in idr1-1 mutant under drought-stressed conditions. Besides, idr1-1 mutant showed reduced expression of OsBRD1. Altogether, these results suggest that mutation of IDR1 leads to alterations of multiple layers of regulations, which ultimately confers obviously enhanced drought tolerance to the idr1-1 mutant.localized in nucleus and to plasma membrane or cell periphery. Further investigations indicated that the significantly increased drought tolerance in idr1-1 mutant stemmed from a range of physiological and morphological changes, including greater leaf potentials, increased proline contents, heightened leaf thickness, and upregulation of antioxidant-synthesizing and drought-induced genes, etc., under drought-stressed conditions. Especially, ROS production might be remarkably impaired, while ROS-scavenging ability appeared to be markedly enhanced as a result of significantly elevated expression of ROS-scavenging enzyme genes in idr1-1 mutant under drought-stressed conditions. Besides, idr1-1 mutant showed reduced expression of OsBRD1. Altogether, these results suggest that mutation of IDR1 leads to alterations of multiple layers of regulations, which ultimately confers obviously enhanced drought tolerance to the idr1-1 mutant.
