Hypoxia-induced transcriptional reprogramming in sugar beet seedlings: Linking energy conservation and metabolic maintenance.

Sugar beet (Beta vulgaris L.), as a major sugar crop, faces a significant threat to its yield and industrial development due to hypoxia stress, a critical environmental factor limiting its growth. Here, we investigate the response mechanisms of sugar beet leaves and roots to hypoxia stress at different developmental stages (first and third true leaf stages). Hypoxia significantly reduced plant height, leaf area, and root area. Key photosynthetic parameters, including net photosynthetic rate, stomatal conductance, and intercellular CO2 concentration, decreased, leading to impaired photosynthetic efficiency. Concurrently, relative electrical conductivity (REC) and malondialdehyde (MDA) content increased, while the activities of antioxidant enzymes such as peroxidase were enhanced. In leaves, only polyphenol oxidase2 (PPO2) was up-regulated under stress, whereas the expression of key chlorophyll synthesis genes was down-regulated to conserve energy. In roots, energy conservation was achieved through the suppression of key genes involved in energy-consuming pathways, such as gluconeogenesis and the glycine betaine synthesis pathway. Conversely, sugar beet adapted to the hypoxic environment by inducing the up-regulated expression of genes including pyruvate decarboxylase 1 (PDC1), aldehyde dehydrogenase 7 (ALDH7), and alcohol dehydrogenase 7 (ADH7), which are predicted to function in detoxifying harmful aldehydes, potentially reducing their toxic accumulation within cells. These results indicate the existence of organ-specific transcriptional responses in sugar beet. Overall, our findings provide molecular insights into the hypoxic response in sugar beet and reveal key physiological and gene regulatory targets for enhancing waterlogging tolerance, thereby contributing to a deeper understanding of plant adaptation mechanisms under oxygen-deficient conditions.