Molecular mechanisms and future improvement of submergence tolerance in rice

Rice is one of most important crops in the world and is also the most advanced crop for breeding among cereal crops. Generally, rice is grown in lowland and flood-prone areas due to its ability to survive in semiaquatic environments. To adapt to excess water conditions, rice has developed specialized anatomical and morphological traits such as aerenchyma, radial oxygen loss barriers, adventitious roots, and leaf gas film formation ability. However, these strategies are insufficient for survival under continuous complete submergence, which leads to death due to oxygen starvation. To overcome prolonged submergence, some Asian rice varieties have further developed additional traits such as aerobic germination, quiescence of leaf elongation in response to flash floods, and internode elongation under periodic flooding. In this review, we describe recent progress in the understanding of the various molecular mechanisms and genetic factors regulating flooding tolerance in rice.