Genetic Manipulation of Phytohormone Levels in Sugar beet

The improvement of the commercial sugar beet crop by genetic modification will require the subtle regulation of expression of foreign genes in the transgenic plants. A strategy has been defined for production of high sucrose yield/ high juice purity/ low environmental impact varieties of sugar beet. This requires modification of the phytohormone levels in the outer cambial rings of the storage root. The auxin IAA has been implicated in the development of cambial rings in the sugar beet storage root. The hairy root transformation system was used to introduce the auxin biosynthetic genes (iaaM and iaall) from Agrobacterium rhizogenes strain A4b. Agropine and mannopine were detected in all A4h hairy root clones tested, suggesting transfer (and functional expression) of genes from the Ri plasmid T R T-DNA to the sugar beet genome. It was shown by DNA-DNA hybridisation experiments that part of the TL and TR T-ONA had been integrated into the sugar beet cv. Bella genome. Altered levels of IAA were observed between transformed and non-transformed sugar beet seedling root material and also between different hairy root clones. Preliminary studies on the auxin binding proteins of A4b transformed sugar beet hairy root clones, suggested that there may be a regulatory system to compensate for the excess levels of IAA in transformed tissue. Those clones with the highest level of IAA, in general had lower ABP activity. The hairy root transformation system was a suitable model for introducing the auxin biosynthetic genes of Agrobacterium in order to alter plant growth regulator levels within the sugar beet cv. Bella genome.