Dro1, a Quantitative Trait Locus Involved In Deep Rooting, Enhances Drought Avoidance In Rice

Drought is the main abiotic stress that limits crop production under rain-fed conditions. The survival of most terrestrial plants depends on the ability of roots to obtain water from the soil. Under drought conditions, water is found disproportionately in deep soil layers. Consequently, deeper rooting appears to be an efficient strategy for avoiding drought stress because it enables a plant to absorb more water from the deep soil layers. In this study, we cloned and characterized a quantitative trait locus for deep rooting: Deeper rooting 1 (Dro1). Dro1 encodes an unknown protein that is expressed in root tips, especially, the cell division zone. 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 cell division in the root tip that causes asymmetric root growth as the root bends in response to gravity. Greater Dro1 expression increases the root growth angle, i.e., roots grow in a more downward direction. We developed a near-isogenic line for Dro1 (Dro1-NIL) with the IR64 genetic background to elucidate the effect of Dro1 on drought avoidance. IR64 and Dro1-NIL were exposed to drought stress under upland conditions. The yield of Dro1-NIL was significantly higher than that of IR64, demonstrating that Dro1 contributes to drought avoidance in rice and can improve productivity under drought conditions.