ABSTRACT

Hairy root disease is a rooty proliferation induced by Agrobacterium rhizogenes in dicotiledoneus plants caused by the insertion of a Ri plasmid fragment in the plant’s genome. This fragment, called T-DNA, consists of several genes limited by two 25bp or border sequences, which are required for the transfer of genes found between them. Amongst these transferable genes stand out ORFs 10, 11 and 12 (rolA, rolB, rolC) because they are most essential for the root induction, and ORFs 8, 13, 14 because they are the most conserved genes of all known Ri plasmids.

The open reading frame 8 (ORF8) of different pRi is still little known. The fact that this gene has evolved less than ORFs 10, 11 and 12, which are essential, suggests that it encodes important functions that would explain the little sequence variability.

As ORF8 expression from cucumopine type A. rhizogenes strain (pRi2659)is higher in roots  than leaves in this work we have studied growth and alkaloid production of four kinds of tobacco roots: wild type tobacco roots (WT), pRi2659 ORF8 transgenic tobacco roots(ORF8), tobacco roots habouring the whole T-DNA from pRiA4 (WT-A4) and finally transgenic roots habouring both the pRi2659 ORF8 and the whole T-DNA from pRiA4 (ORF8-A4). We have used ORF8 under the control of the 35S RNA promoter.

ORF8 transgenic roots had less growth than wild type roots, but alkaloid production was similar in both; WT-A4 and ORF8-A4 roots had more growth than wild and ORF8 type roots, and their production was also higher. There is a relationship between alkaloid production and biomass in the four types of roots.

It is suggested that pRi2659 ORF8 acts in the primary metabolism, in someway related with the auxin sensibility.