Enhanced stress tolerance in transformed Ajuga bracteosa Wall. ex Benth. regenerants by upregulated gene expression of metabolic pathways

Abstract

The rol oncogenes of Agrobacterium rhizogenes enhance the production of medicinally important compounds in plants andprovide a first barrier against the overproduction of reactive oxygen species during biotic and abiotic stress. This study was designed toevaluate the expression of genes involved in biosynthetic pathways and their impact on metabolic contents and environmental stresstolerance in regenerated Ajuga bracteosa Wall. ex Benth. After successful transformation, real-time quantitative PCR confirmed theincreased expression (1.94–6.59-fold) of HMGR, HDS, FDS, PAL, and TTG1 genes in transgenic lines. Furthermore, GC-MS coupledwith principal component analysis revealed diverse concentrations of 97 metabolites in A. bracteosa. Transgenic lines showed greatersurvival under multiple stresses. This was revealed by significant chlorophyll content (8.13–21 µmoles/m2), higher quantum efficiencyof PSII ($F_{v/;}F_m$), and the performance index ($PI_{abs}$) value. Similarly, catalase and peroxidase enzyme activities were enhanced duringextreme drought (300–400 mM mannitol) and salinity (150–200 mM NaCl) conditions, compared to untransformed control. Wildtype control plant leaves were completely necrotized by Aspergillus fumigatus (FCBP 66) and Fusarium solani (FCBP 0291), whereastransformed leaves had improved antifungal resistance. In conclusion, our data suggest that rolABC genes have a significant impact onthe synthesis of metabolites involved in enhancing multistress tolerance in A. bracteosa.