AGROBACTERIUM RHIZOGENES ROLB GENE IMPROVES PHOTOSYNTHESIS AND PHOTOPROTECTION UNDER FAR-RED LIGHT IN TRANSGENIC TOMATO PLANTS

Previous work showed in tomato plants harbouring the Agrobacterium rhizogenes rolB gene overexpression of genes involved in chloroplast function and stress response, significant increase in non-photochemical quenching and chlorophyll a and b content, and reduced chlorophyll a/b ratio. The latter condition being typical of plant shade, where far-red is dominant, suggested a role for rolB in improving photosynthesis in such condition. To gain a better insight into these results, we evaluated the photosynthetic performance of transgenic and control plants after 6 days-exposure to a far-red-enriched light source by chlorophyll a fluorescence kinetics. Photosynthetic parameters were determined, as well as chlorophyll a and b content. Real-time PCR was also performed to quantify the expression level of some of the chloroplast-related genes already shown to be overexpressed in rolB plants. Results showed in transgenic plants improved photochemical efficiency under far-redenriched light regimen with respect to control plants. Photoprotection capability on the other hand was higher in rolB plants in both light conditions, but in far-red-enriched condition differences were prominent. Chlorophyll a/b ratio was decreased in transgenic plants under far-red-enriched light with respect to white light. Finally, qPCR showed that the expression of genes encoding chloroplast small heat shock protein, chlorophyll a/b binding protein and carbonic anhydrase was significantly induced by far-red-enriched condition. Taken together, these data suggest the involvement of rolB in photosynthesis modulation under far-red-rich light in tomato, an adaptive behaviour similar to that of sciaphilous plants.