Abstract
The heterogeneous distribution of soil salinity across the rhizosphere can moderate salt injury and improve sorghum growth. However, the essential molecular mechanisms used by sorghum to adapt to such environmental conditions remain uncharacterized. The present study evaluated physiological parameters such as the photosynthetic rate, antioxidative enzyme activities, leaf Na+ and K+ contents, and osmolyte contents and investigated gene expression patterns via RNA sequencing (RNA-seq) analysis under various conditions of nonuniformly distributed salt. Totals of 5691 and 2047 differentially expressed genes (DEGs) in the leaves and roots, respectively, were identified by RNA-seq under nonuniform (NaCl-free and 200 mmol·L-1 NaCl) and uniform (100 mmol·L-1 and 100 mmol·L-1 NaCl) salinity conditions. The expression of genes related to photosynthesis, Na+ compartmentalization, phytohormone metabolism, antioxidative enzymes, and transcription factors (TFs) was enhanced in leaves under nonuniform salinity stress compared with uniform salinity stress. Similarly, the expression of the majority of aquaporins and essential mineral transporters was upregulated in the NaCl-free root side in the nonuniform salinity treatment, whereas abscisic acid (ABA)-related and salt stress-responsive TF transcripts were more abundant in the high-saline root side in the nonuniform salinity treatment. In contrast, the expression of the DEGs identified in the nonuniform salinity treatment remained virtually unaffected and was even downregulated in the uniform salinity treatment. The transcriptome findings might be supportive of the increased photosynthetic rate, reduced Na+ levels, increased antioxidative capability in the leaves and, consequently, the growth recovery of sorghum under nonuniform salinity stress as well as the inhibited sorghum growth under uniform salinity conditions. The increased expression of salt resistance genes activated in response to the nonuniform salinity distribution implied that the cross-talk between the nonsaline and high-saline sides of the roots exposed to nonuniform salt stress is potentially regulated.
Highlights
Crop yields are significantly challenged by an extensive range of environmental constraints
Given the expression profiles from the RNA sequencing (RNA-seq) data, differentially expressed genes (DEGs) were determined if the fold change in their expression was 2 and if their false discovery rate (FDR) value was 0.01
Our results showed that most plasma membrane intrinsic proteins (PIPs) and tonoplast intrinsic proteins (TIPs) transcription was inhibited under both salinity conditions but remained almost unchanged under nonsalinity conditions, suggesting a probable transcriptomic tuning of aquaporins to maintain water uptake through the nonsaline rhizosphere of seedlings in nonuniform saline environments
Summary
Crop yields are significantly challenged by an extensive range of environmental constraints. 80 million hectares of global agricultural land have been salinized [2]. Inappropriate human production and agricultural activities have been exacerbating soil salinization by 10% annually, at which pace more than half of the global cultivated land today will be affected by soil salinity by 2050 [3]. High soil salt concentrations can cause osmotic stress and ionic toxicity, which result in slowed growth, reduced productivity, dysfunctional metabolism and excess production of reactive oxygen species (ROS) due to water/nutrient uptake deficiencies, and disturbed Na+/K+ ratios [3,4,5]. To combat high soil salinity, plants have evolved many endogenous mechanisms to alleviate the deleterious effects of salt damage and water/nutrient deficiency
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