Key Heat-responsive Genes and Pathways in Tropical and Temperate Maize (Zea mays) Germplasms as Revealed by Physiological and Transcriptome Analyses

Heat stress is becoming a severe threat to maize yield worldwide. Confirmation of the maize germplasm tolerant to heat still remains elusive. In this study, we investigated physiology and transcriptomic profiling in the heat stress response among four different genotypes derived from the tropical and temperate maize germplasms. High temperatures induced pronounced increase in peroxidase (POD) and superoxide dismutase (SOD) activities, and malondialdehyde (MDA), soluble carbohydrate, and protein contents, but there were dramatic reductions in the chlorophyll content and four chlorophyll fluorescence parameters for the four maize genotypes. Heat stress had smaller effects on tropical maize genotypes compared to temperate genotypes. The RNA-seq analysis resulted in 44.5-54.0 million raw reads. A total of 44,241 global expression genes (almost 96.12% of the whole gene-set) were detected and many DEGs associated with specific genotypes were identified. Pairwise comparison between the genotypes revealed that 805 differentially expressed genes (DEGs) were shared. The gene ontology (GO) terms, such as signaling, cellular component organization, cellular component biogenesis, macromolecular complex, molecular transducer activity and structural molecule activity were commonly overrepresented in four genotypes under heat stress. The analysis of DEGs related to stress responses indicated that several crucial genes involved in heat stress were highly up-regulated, and the remaining up-regulated genes were found to be consistently expressed in the four genotypes, showing that the tropical and temperate maize germplasms had similar gene expressions in response to high temperatures. Our findings showed that tropical germplasms conferred potential heat-intolerance. (C) 2020 Friends Science Publishers