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

Agrobacterium rhizogenes, chlorophyll fluorescence, far-red, rol genes, Solanum lycopersicum 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.