Physiological, biochemical and transcriptomic studies reveal the mechanisms promoting tiller bud growth under high temperature conditions in japonica rice

Abstract

High temperature (HT) negatively impacts the initiation and development of tiller buds in japonica rice, resulting in a substantial decrease in yield. However, the physiological and molecular mechanisms alleviating the inhibition of HT on the growth of tiller buds in japonica rice remain elusive. Hence, this study aimed to dissect the underlying mechanisms of normal tiller buds’ growth under HT in japonica rice through comparative physiological, biochemical and transcriptomics analyses of two contrasting varieties, ‘Changgeng 225’ (‘CG225’, heat-tolerant) and ‘Zhonghua 11’ (‘ZH11’, heat-sensitive). Compared with ‘ZH11’, the tiller number of ‘CG225’ decreased less under HT stress. ‘CG225’ outperformance over ‘ZH11’ was due to higher activities of the antioxidant enzymes (SOD, CAT, POD and APX), as well as higher activities of the key enzymes involved in carbon and nitrogen metabolism (NR, GOGAT, GS, GDH, SS and SPS) in tiller buds. In addition, lower contents of the tiller-inhibiting phytohormone ABA and SLs, and higher contents of the tiller-promoting phytohormone CK in ‘CG225’ also promoted the growth of tiller buds. Most of the significant DEGs between ‘CG225’ and ‘ZH11’ under HT conditions were assigned to chloroplast and photosynthesis. We identified potential candidate genes, including transcription factors (EP2, B3, bHLH, MYB, NAC, and WRKY), phytohormone (auxin efflux carriers and ethylene biosynthesis genes), antioxidant system (peroxidases), and sucrose pathway-related genes. Furthermore, ectopic sucrose application significantly alleviated HT inhibitory effects on tiller bud growth of ‘ZH11’ plants. Our results reveal a synergistic control of heat stress by several metabolic mechanisms in japonica rice during tillering and provide fundamental resources for improving rice HT tolerance and production.