Genetic transformation and regeneration of plant overexpressing CuZnSOD gene to control oxidative stress in rubber tree

Hevea brasiliensis is the main source of natural rubber which is biosynthesized in latex cells. The high metabolic productivity required for latex regeneration after each tapping can be enhanced by ethylene application, which optimizes the production potential in rubber tree. However, excessive metabolism activation can lead to Tapping Panel Dryness (TPD). Expression analyses of many genes involved in detoxifying the reactive oxygen species (ROS) have been studied in healthy trees, TPD trees and also in young budded plants. Among them, the gene encoding CuZnSOD displays a differential expression in the three genotypes and in response to normal photosynthesis occurring during the day, in response to ethylene and wounding in young budded plants. Indeed, during photosynthesis, ROS production is intense and CuZnSOD gene expression is slightly stimulated in PB260 at 4.00 pm and highly stimulated at 12.00 am in PB217 and RRIM600. In response to ethylene, CuZnSOD gene expression is slightly stimulated in PB260 and PB217 but repressed in RRIM600 even if the expression level is higher. Moreover, CuZnSOD transcript level is reduced in response to wounding. As the CuZnSOD gene has been shown to be also less expressed in tree affected by TDP, it was over-expressed under the CaMV35S promoter in friable calli of the genotype PB260 by an Agrobacterium tumefaciens-mediated genetic transformation using the GFP visual marker. The calli containing one insertion of the T-DNA have been selected and the over-expression of the CuZnSOD gene checked. Plants are now acclimated in the green house and their response to abiotic stress will be analysed.