Pyramiding of γ-TMT and gly I transgenes in Brassica juncea enhances salinity and drought stress tolerance

We previously generated Brassica juncea lines overexpressing either glyoxalase I (gly I) or γ-tocopherol methyltransferase (γ-TMT) involved in the glyoxalase system and tocopherol biosynthesis, respectively. These transgenic plants showed tolerance to multiple abiotic stresses. As tolerance is a complex trait that can be improved by pyramiding of several characteristics in a single genotype, we generated in this study B. juncea plants coexpressing gly I and γ-TMT by crossing the previously generated stable transgenic lines. The performance of the newly generated B. juncea lines coexpressing gly I and γ-TMT was compared with that of wild-type and the single transgenic lines under non-stressed and NaCl and mannitol stress conditions. Our results show a more robust antioxidant response of B. juncea plants coexpressing gly I and γ-TMT compared to the other lines in terms of higher chlorophyll retention, relative water content, antioxidant enzyme and proline levels, and photosynthetic efficiency and lower oxidative damage. The differences in response to the stress of the different lines were reflected in their yield parameters. Overall, we demonstrate that the pyramiding of multiple genes involved in antioxidant pathways could be a viable and useful approach for achieving higher abiotic stress tolerance in crop plants.