Genome-wide analysis of gene expression profiles during early ear development of sweet corn under heat stress

Heat stress is one of the limiting factors for the production of sweet corn in southern China, influencing ear formation and reducing yield. Identification of relationships between heat responses and genetic regulatory mechanisms is of great significance to breeding for heat tolerance and production of summer planted sweet corn. In this study, DGE (digital gene expression) was used to investigate the global gene expression profiles for early ear development of the sweet corn cultivar Yuetian 13' under heat stress. Results indicated that, in the distribution of total clean tags, high-expression tags with copy numbers larger than 100 were in absolute dominance, whereas low-expression tags with copy numbers smaller than five occupy the majority of distinct tag distributions. Further functional annotation of differentially expressed genes showed that 17893 genes could be categorized into three main groups. Of them, 13.7% were distributed in cell parts, intracellular, organelle, cytoplasm and membrane in cellular component category, 26.6% possessed catalytic, binding, hydrolase, and transferase and oxidoreductase activities in the molecular function category, and 59.7% were involved in metabolic processes, cellular processes, responses to stimuli, and transport and biological regulation in the biological process. A total of 949 significantly differential expression genes were detected, including 705 upregulated and 244 downregulated. Among them, 108 and 40 genes were upregulated and downregulated at least 10-fold. Under heat stress, the genes related to maintenance of cell structure, photosynthesis, signal transduction, transcription factors and response to stress with higher expression levels in the ear might be valuable for understanding early kernel and ear development. Deep research on characterizing differentially expressed genes with unknown functions will lay the foundation for further identification of genetic regulatory mechanisms under heat stress.