Abstract
Land plants evolve drought acclimation. Existing knowledge of gene regulation mainly comes from short-term drought treatment. However, common regulatory mechanism shared by multiple varieties under long-term drought is little explored. Here we investigated changes in physiology, hormones and transcriptomes in leaves of Nicotiana varieties K326 and Basma Xanthi with/without drought treatment at time courses spanning 1 month. Analyses of deep RNA-Seq data and further full-length Iso-Seq data revealed an atlas of dynamic changes of transcripts, spliced isoforms, gene expression, associated Gene Ontology, and metabolism pathways. Fewer differentially expressed genes (DEGs) were induced by drought in high tolerance variety than susceptible variety. Comparison among seven hormone signal pathways identified that genes in both abscisic acid and auxin signaling pathways were highly induced although specific genes were depended on the variety. Common hormone regulatory network analysis revealed that genes encoding clade A protein phosphatase 2C gene (PP2C) in abscisic acid pathway was the pivotal hub. Expressional regulation in photosynthesis was also common and variety specific. We conclude that long-term drought inducing gene regulatory networks of hormones and photosynthesis are variety dependent, and PP2C is the center of the common hormone regulatory network. Thus, this study improves our understanding of gene regulatory network in drought response.
Highlights
Plants have evolved to adapt to environmental stresses
These phenotypic changes suggest that the drought treatment inhibits vertical growth and leaf expansion, but the tolerance to drought is higher in BX than in K326
Since hormone signal transduction pathways were enriched by differentially expressed genes (DEGs), we further investigated the regulation of these DEGs. 51 and 50 DEGs were identified in varieties K326 and BX, respectively, which were involved with seven hormones including abscisic acid (ABA), auxin, cytokinin, gibberellin, brassinosteroid, jasmonic acid, and ethylene (Figure 3)
Summary
Plants have evolved to adapt to environmental stresses. Drought, or water deficit, is one of the most adverse abiotic stresses and reduces terrestrial plant productivity, threatening our food security. Increasing transcriptome profiles have revealed some transcriptional regulations under drought, including hormone signaling genes and transcription factors (Shanker et al, 2014; Burgess and Huang, 2016; Tang et al, 2017). Some studies on long-term drought reveal a typic developmental inhibition and regulations on many genes’ expression, e.g., genes for transcription factor, carbohydrate metabolism and signal transduction, in several species e.g., in oak (Spieß et al, 2012), Arabidopsis (Su et al, 2013) and Populus (Yan et al, 2012). Many proteins were found to be regulated after 30 days of different water deficit regimes compared with those in well-watered control in casava (Shan et al, 2018) Those knowledges of existing long-term studies were mainly from comparisons between after treatment and before treatment after a long time. To increase a power to identify global and conserved regulatory mechanisms, two varieties of N. tabacum and long-term drought treatment with well-watered control will be preferred
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