Abstract
Drought stress is one of the most important abiotic factors limiting crop productivity. A better understanding of the effects of drought on millet (Setaria italica L.) production, a model crop for studying drought tolerance, and the underlying molecular mechanisms responsible for drought stress responses is vital to improvement of agricultural production. In this study, we exposed the drought resistant F1 hybrid, M79, and its parental lines E1 and H1 to drought stress. Subsequent physiological analysis demonstrated that M79 showed higher photosynthetic energy conversion efficiency and drought tolerance than its parents. A transcriptomic study using leaves collected six days after drought treatment, when the soil water content was about ∼20%, identified 3066, 1895, and 2148 differentially expressed genes (DEGs) in M79, E1 and H1 compared to the respective untreated controls, respectively. Further analysis revealed 17 Gene Ontology (GO) enrichments and 14 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways in M79, including photosystem II (PSII) oxygen-evolving complex, peroxidase (POD) activity, plant hormone signal transduction, and chlorophyll biosynthesis. Co-regulation analysis suggested that these DEGs in M79 contributed to the formation of a regulatory network involving multiple biological processes and pathways including photosynthesis, signal transduction, transcriptional regulation, redox regulation, hormonal signaling, and osmotic regulation. RNA-seq analysis also showed that some photosynthesis-related DEGs were highly expressed in M79 compared to its parental lines under drought stress. These results indicate that various molecular pathways, including photosynthesis, respond to drought stress in M79, and provide abundant molecular information for further analysis of the underlying mechanism responding to this stress.
Highlights
Drought is one of the main abiotic stresses that affect global crop production
These results demonstrated that M79 had better tolerance to drought stress than its parental lines as shown by phenotypical and physiological indexes
Among the differentially expressed genes (DEGs) that we identified from three drought-treated cultivars, four genes encoding calmodulin dependent protein kinases (CAMK) kinases were up-regulated, three genes encoding WAK receptor kinases were down-regulated, and seven phosphatase 2C (PP2C) genes were up-regulated in all three cultivars (Table S9)
Summary
Drought is one of the main abiotic stresses that affect global crop production. RNA-seq technology has been widely used to study how stress factors affect transcriptome in crops such as maize (Zhang et al, 2013), wheat (Camilios-Neto et al, 2014), rice (Zhou et al, 2016), sorghum (Fracasso, Trindade & Amaducci, 2016), and foxtail millet (Qi et al, 2013; Yadav, Khan & Prasad, 2015; Yi, Chen & Yu, 2015; Wang et al, 2016b). Qi et al (2013) identified 2824 genes and 215 miRNAs that respond to osmotic stress; while Yadav, Khan & Prasad (2015) found 55 known and 136 new miRNAs differentially expressed genes in two millet varieties after treating plants with 20% PEG-6000 to induce dehydration stress. Wang et al (2016b) found that the millet variety An04-4783 expressed 81 known miRNAs and 72 new miRNAs under drought stress. These reports provide important information on drought responsive mechanisms and related regulatory networks in millet
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