Overexpression of phosphoenol pyruvate carboxylase gene of Flaveria trinervia in transgenic mulberry (Morus spp.) leads to improved photosynthesis rate and tolerance to drought and salinity stresses

This study developed three transgenic mulberry lines containing heterologous phosphoenol pyruvate carboxylase gene of Flaveria trinervia through Agrobacterium tumefaciens-mediated genetic transformation using cotyledon and hypocotyl explants of mulberry cv. G4. These transgenic lines had 1-1.56-fold expression of the phosphoenol pyruvate carboxylase gene of Flaveria trinervia, regulated by a constitutive promoter. The phosphoenol pyruvate carboxylase activity in transgenic mulberry lines enhanced upto 1.91 to 2.66-fold compared to wild-type plants. Transgenic mulberry lines exhibited significantly higher photosynthetic rate, improved instantaneous water use efficiency, stomatal conductance, transpiration rate, relative water, and proline content than the WT plants under 60% field capacity. Leaf discs assay of transgenic lines revealed less chlorophyll degradation and electrolyte leakage than those in wild-type plants under 25% polyethylene glycol (molecular weight > 6000) and 200 mM NaCl. In this study, for the first time, transgenic mulberry lines expressing the phosphoenol pyruvate carboxylase gene of Flaveria trinervia were developed, which showed improved photosynthesis rate with tolerance to drought and salinity stresses. These transgenic mulberry lines developed in this study could be further tested in a confined field trial to evaluate their leaf yield, yield attributes, leaf quality, and physiological parameters under irrigated and sub-optimal irrigation/drought stress conditions. These transgenic lines could be used as pre-breeding resources in mulberry breeding programs in the future.