The vacuolar proton pyrophosphatase gene (SbVPPase) from the Sorghum bicolor confers salt tolerance in transgenic Brahmi [Bacopa monnieri (L.) Pennell]

Plants overcome the effect of Na+ toxicity either by excluding Na+ at the plasma membrane or by sequestering them into the vacuoles. Influx of Na+ ions into the plant vacuoles is usually driven by H+ generated by vacuolar-type H+-ATPase as well as vacuolar proton pyrophosphatse (VPPase). In the present study, we have developed Bacopa monnieri transgenics via Agrobacterium tumefaciens containing the recombinant vector pCAMBIA2300-SbVPPase gene. Transformants were produced using nodal explants. Transformants were confirmed by PCR and DNA blot analysis. qPCR analysis showed higher transcript levels of SbVPPase compared to untransformed control (UC). Higher VPPase activity was recorded in transgenics compared to UC. Under 150 mM salt stress, transgenic shoots showed enhanced Na+ accumulation with better biomass production, increased glycine betaine content, and total soluble sugar levels than UC. Transgenic shoots showed 2.9-3.8-folds lower levels of malondialdehyde content indicating lesser membrane damage. Increase in antioxidant enzyme activities (1.4-3.2-folds) was observed in transgenics compared to UC. Transgenics also displayed 7.3-9.0-folds enhanced accumulation of the medicinally important compound bacoside A. Increased biomass production, accumulation of Na+, osmolytes (glycine betaine, sugars etc.), and elevated antioxidant enzyme activities indicate better osmotic adjustment in transgenics by compartmentalization of Na+ into the vacuoles under salt stress conditions. Thus, overexpression of SbVPPase in Bacopa alleviated salt stress by sequestering Na+.