Available online at www.sciencedirect.com Rice growth adapting to deepwater Yoko Hattori 1 , Keisuke Nagai 1,2 and Motoyuki Ashikari 1 Flooding is one of the most hazardous natural disasters, and there are several levels of flooding. Recently, research on flood- tolerant rice plants revealed that some rice varieties have evolved to overcome two different flood types, ‘flash flood’ and ‘deepwater flood’, using two different mechanisms, and their molecular mechanisms were determined. During flash flooding, the tolerant plants that are fully submerged for a few weeks stop elongating and thus avoid energy consumption that will be needed to restart growth when the water recedes. On the contrary, during deepwater flooding, with water depth up to several meters for several months, the deepwater-flood- tolerant rice plants promote elongation of internodes to keep the foliage above the water surface and thus allow respiration and photosynthesis. Addresses 1 Bioscience and Biotechnology Center, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8601, Japan 2 Research Fellow of the Japan Society for the Promotion of Science, Sumitomo-Ichibancho Bldg., 6 Ichibancho, Chiyoda-ku, Tokyo 102- 8471, Japan Corresponding author: Ashikari, Motoyuki (ashi@agr.nagoya-u.ac.jp) Current Opinion in Plant Biology 2011, 14:100–105 This review comes from a themed issue on Growth and development Edited by Jiayang Li and Nam-Hai Chua Available online 8th October 2010 1369-5266/$ – see front matter # 2010 Elsevier Ltd. All rights reserved. DOI 10.1016/j.pbi.2010.09.008 Introduction There are many different environments on Earth, some of which constitute severe and adverse environmental con- ditions for living organisms. Therefore, living organisms have developed many biological functions to overcome such severe environmental conditions and have suc- ceeded in adapting to many unfavorable environments. Unlike motile organisms, plants are sedentary and cannot move rapidly in response to sudden environmental changes. Thus, plants must face environmental altera- tions directly and establish new adaptation mechanisms to overcome hostile environments. At the same time, plants must expand their habitats for the continuation of their species and avoiding competition with other species. Over their long evolutionary history of habitat expansion, plants have faced many kinds of severe environmental conditions, such as deserts, brackish-water regions, high altitude and hot or cold climates. Over this long time, plants have evolved through natural selection, gaining new adaptations and increased diversity, and have succeeded in expanding their habitats. Water is essential for all life, and living in a watery environment, such as rivers, lakes and swamps, can be an advantage for plants and animals. However, living beside water also involves the risk of sudden flooding or long periods of flooding after heavy rain. Flooding is a natural disaster which causes growth inhibition and great reduction of yield. Common rice (Oryza sativa L.) culti- vars are generally planted in dry or irrigated areas, and are comparatively tolerant to water compared to other crop plants, such as maize and wheat [1]. However, rice does not have complete tolerance to flooding, and if it is completely submerged or flooded for long periods, plants die due to oxygen starvation and energy depletion [2]. Flooding levels vary, depending on the amount and duration of rain, underlying geological formations and distance from the water. Among these factors, there are two typical kinds of flood. One is short duration over a few weeks and not very deep, termed a ‘flash flood’ (Figure 1a) and the other is deep flooding that lasts for a long time, a ‘deepwater flood’ (Figure 1b). Recent studies have revealed that rice plants have adapted to these two forms of flooding through different tolerance mechanisms (Figure 1). Many agronomic traits, including tolerance to flash and deepwater floods, are expressed in continuous phenotypic variations. These complex traits are generally governed by some or many genes, that is quantitative trait loci (QTL), derived from natural variations in the plant [3,4]. QTL analysis has been used as a powerful tool to discover complex traits and help in the initial step of cloning the genes [5–9]. Progress in obtaining genomic information as well as new tools [10,11] has greatly facilitated QTL analysis in rice. In this review, we focus on rice avoidance and elongation strategies, and discuss the molecular mechanisms involved. Quiescence under flash flood Tolerance to flash flood (i.e. submergence tolerance) is defined as ‘the ability of a rice plant to survive 10–14 d of complete submergence and renew its growth when the water subsides...’[12  ]. Flash floods are unexpected and uncontrollable, and its flooding water level can reach 50 cm in the rain-fed lowlands of the humid and semi- humid tropics of South and Southeast Asia. In these areas, flash floods at the seedling stage of rice cause severely reduced yields of rice grain [12  ]. However, some rice Current Opinion in Plant Biology 2011, 14:100–105 www.sciencedirect.com