Abstract
The transgenic technology using a single gene has been widely used for crop improvement. But the transgenic pyramiding of multiple genes, a promising alternative especially for enhancing complexly inherited abiotic stress tolerance, has received little attention. Here, we developed and evaluated transgenic rice lines with a single Salt Responsive Protein 3-1 (SaSRP3-1) gene as well as pyramids with two-genes SaSRP3-1 and Vacuolar H+-ATPase subunit c1 (SaVHAc1) derived from a halophyte grass Spartina alterniflora L. for salt tolerance at seedling, vegetative, and reproductive stages. The overexpression of this novel gene SaSRP3-1 resulted in significantly better growth of E. coli with the recombinant plasmid under 600 mM NaCl stress condition compared with the control. During early seedling and vegetative stages, the single gene and pyramided transgenic rice plants showed enhanced tolerance to salt stress with minimal wilting and drying symptoms, improved shoot and root growth, and significantly higher chlorophyll content, relative water content, and K+/Na+ ratio than the control plants. The salt stress screening during reproductive stage revealed that the transgenic plants with single gene and pyramids had better grain filling, whereas the pyramided plants showed significantly higher grain yield and higher grain weight compared to control plants. Our study demonstrated transgenic pyramiding as a viable approach to achieve higher level of salt tolerance in crop plants.
Highlights
The productivity of rice (Oryza sativa L.) and other food crops is severely affected by abiotic stresses such as drought, salinity, flooding, temperature extremes, and nutrient deficiency or toxicity worldwide
Amino acid analysis indicated that 44 amino acids were hydrophobic in SaSRP3-1 and 14 to 28th amino acids formed a single hydrophobic transmembrane domain (TMD) (Supplementary Figure S1D)
The presence of a single TMD indicated the possibility of unique plasma membrane protein (PMP) evolution in S. alterniflora to form an uncharacterized but crucial protein to survive under abiotic stress environments
Summary
The productivity of rice (Oryza sativa L.) and other food crops is severely affected by abiotic stresses such as drought, salinity, flooding, temperature extremes, and nutrient deficiency or toxicity worldwide. Since salt tolerant traits are controlled by many genes and influenced by environmental interactions (Flowers et al, 2000; Koyama et al, 2001; Lin et al, 2003), the development of salt tolerant varieties through marker assisted selection (MAS) requires extensive genotyping efforts and longer time to introgress many desirable QTLs into elite cultivars. Smooth cordgrass is a halophytic grass species widely grown in coastal salt marsh areas of the United States. It can grow well in areas, where salinity is a major obstacle for plant growth. Transgenic rice plants overexpressing a soluble inorganic pyrophosphatase gene ThPP1 of Thellungiella halophila showed enhanced tolerance to alkaline stress compared to the wild type (He et al, 2017)
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