Sugar Starvation of Rice Anthers is a Factor in Reproductive Failure under Heat and Drought Stress, as shown by Metabolite and Transcript Profiling

Abstract

Due to global climate change, heat and drought stress have an increasing impact on rice (Oryza sativa L.) yields and become major challenges in agriculture. Severe yield losses were observed when a single stress or a combination of stresses coincide with flowering, but the physiological responses of rice floral organs leading to spikelet sterility are not known. Metabolic and transcriptomic profiling of anthers, pistils before pollination and pollinated pistils was performed to investigate physiological responses determining fertility under heat and combined drought and heat stress using the heat- and drought-tolerant N22 and the heat-sensitive and drought-tolerant cultivar Moroberekan. Different metabolite patterns were observed between floral organs as well as between cultivars under non-stressed and stressed conditions. Several candidate metabolites were differentially accumulated in stressed anthers of N22 compared to Moroberekan under non- stress conditions. More genes were regulated under heat-drought stress than heat stress in anthers of both cultivars with N22 showing much less gene regulation under combined stress in comparison to Moroberekan. The functional class of genes related to stress was over-represented under all stress conditions in both cultivars while fewer bins were over-represented under heat stress compared to combined stress. Combining metabolite and transcriptomic analyses identified sugar metabolism in anthers as crucial for tolerance or susceptibility to stress. In the future, identification of candidate metabolites and genes will be useful for marker assisted selection procedures to breed more stress tolerant crop plants.