Abstract
Tolerance to salinity is a complex genetic trait including numerous physiological processes, such as metabolic pathways and gene networks; thereby, identification of genes indirectly affecting, as well as those directly influencing, is of utmost importance. In this study, we identified and elucidated the functional characterization of AtPAP17 and AtPAP26 genes, as two novel purple acid phosphatases associated with high-salt tolerance in NaCl-stressed conditions. Here, the overexpression of both genes enhanced the expression level of AtSOS1, AtSOS2, AtSOS3, AtHKT1, AtVPV1, and AtNHX1 genes, involving in the K+/Na+ homeostasis pathway. The improved expression of the genes led to facilitating intracellular Na+ homeostasis and decreasing the ion-specific damages occurred in overexpressed genotypes (OEs). An increase in potassium content and K+/Na+ ratio was observed in OE17 and OE26 genotypes as well; however, lower content of sodium accumulated in these plants at 150 mM NaCl. The overexpression of these two genes resulted in the upregulation of the activity of the catalase, guaiacol peroxidase, and ascorbate peroxidase. Consequently, the overexpressed plants showed the lower levels of hydrogen peroxide where the lowest amount of lipid peroxidation occurred in these lines. Besides the oxidation resistance, the boost of the osmotic regulation through the increased proline and glycine-betaine coupled with a higher content of pigments and carbohydrates resulted in significantly enhancing biomass production and yield in the OEs under 150 mM NaCl. High-salt stress was also responsible for a sharp induction on the expression of both PAP17 and PAP26 genes. Our results support the hypothesis that these two phosphatases are involved in plant responses to salt stress by APase activity and/or non-APase activity thereof. The overexpression of PAP17 and PAP26 could result in increasing the intracellular APase activity in both OEs, which exhibited significant increases in the total phosphate and free Pi content compared to the wild-type plants. Opposite results witnessed in mutant genotypes (Mu17, Mu26, and DM), associating with the loss of AtPAP17 and AtPAP26 functions, clearly confirmed the role of these two genes in salt tolerance. Hence, these genes can be used as candidate genes in molecular breeding approaches to improve the salinity tolerance of crop plants.
Highlights
Salinity is one of the major abiotic factors affecting the growth, development, and productivity of agricultural crops (Munns and Gilliham, 2015; Parihar et al, 2015; Zörb et al, 2019)
A significant increase of the parameters was presented in each overexpressed genotype (OE17 and OE26) in 150 mM NaCl comparing with control plants (Table 2)
Our results showed that knockout mutation of AtPAP17 or AtPAP26 genes led extremely to sense the phosphorus imbalance in Mu17, Mu26, and double mutant (DM) plants imposed to salinity and even normal conditions (0 mM NaCl) compared to wild-type and overexpressed genotypes (OEs) lines at the same condition
Summary
Salinity is one of the major abiotic factors affecting the growth, development, and productivity of agricultural crops (Munns and Gilliham, 2015; Parihar et al, 2015; Zörb et al, 2019). All main processes such as protein synthesis, photosynthesis, and metabolism of lipid and energy are adversely affected by salinity within plants (Woodrow et al, 2017; Zörb et al, 2019). Phosphorus plays an important role in plant’s developmental processes at both cellular and whole plant level comprising respiration, photosynthesis, energy metabolism, membrane biosynthesis, regulation of several enzymes involved in protein synthesis, biosynthesis of nucleic acids, signaling pathways, and ion transport (Plaxton, 2004; Tran et al, 2010a; Malhotra et al, 2018)
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