The private life of deepwater rice: Unravelling exclusive features and unexplored mechanisms

Rice being a major cereal crop of the world, grows across a wide range of climatic conditions, which is why it has evolutionarily adopted diverse adaptations. Among these, deepwater rice (DWR) is the one which is cultivated in very limited places in the world, to such an extent that no other crops can coexist in this particular ecosystem. Evolutionarily, rice has adapted to deep water ecology with some unique anatomical, morphological, physiological, and molecular characteristics. Understanding the mechanisms of survival in the deepwater ecosystem is crucial for identifying genes/quantitative trait loci (QTLs) to develop superior DWR with higher yield and subsequent introgression through marker-assisted breeding approaches. Phenotyping studies have mostly been conducted at 6 to 8 leaf stages, whereas deepwater flood typically begins around one month into the late vegetative stage. More attention is needed to conduct research on DWR at late vegetative or reproductive stages, as well as the factors that determine the threshold level of dissolved O₂ in water which triggers anatomical modifications necessary for efficient gas exchange between aerial and submerged plant organs. More investigations are needed to identify novel genes, proteins, and metabolites regulating tolerance underwater and improve deepwater flood tolerance ability. The unique adaptations of DWR may also be associated with novel alleles related to traits such as nutritional quality and compatibility with natural farming practices. In this article, we provide a comprehensive analysis of recent research findings on unique features of DWR and its adaptation to grow under deepwater conditions, high-yielding DWR varieties developed by rice breeders, and genomic resources such as QTLs, genes, and miRNAs responsible for deepwater adaptation. We also highlight the research gaps as well as a future line of work collectively in this article. In a nutshell, our review will serve as a global reference for DWR research.