Drought is the most serious abiotic stress that hinders rice production under rainfed conditions. To improve drought resistance in rice, molecular breeding of root system architecture(RAS)by using a marker-assisted selection is considered one of the most promising breeding strategies. However, the gene(s)responsible for RSA has not been identified in rice and is still unclear to have its effect on drought avoidance. We cloned DEEPER ROOTING 1(DRO1), a rice quantitative trait locus controlling root growth angle, using mapping populations derived from a cross between IR64, a lowland rice with shallow roots, and Kinandang Patong, an upland rice with deep roots. DRO1 encodes an unknown protein that is expressed in root tips. A putative auxin response element in its promoter region interacted specifically with Auxin Response Factor(ARF), suggesting that ARF regulates DRO1 directly in the auxin signaling pathway. DRO1, which is negatively regulated by auxin, is involved in the root tip that causes asymmetric root growth as the root bends in response to gravity. We developed a near-isogenic line for DRO1(Dro1-NIL)in the IR64 genetic background. The maximum root depth of Dro1-NIL was more than twice that of IR64 under upland condition. The yield of Dro1-NIL was significantly higher than that of IR64 under upland condition with drought. These demonstrate that DRO1 contributes to drought avoidance and can improve productivity under drought conditions. Thus, molecular breeding using gene(s)controlling RSA may be applied to develop new cultivars with high adaptability to drought in other crops.

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