EXPRESSION OF AGROBACTERIUM-RHIZOGENES AUXIN BIOSYNTHESIS GENES IN TRANSGENIC TOBACCO PLANTS

Plant oncogenes aux1 and aux2 carried by the TR-DNA of Agrobacterium r hizogenes strain A4 encode two enzymes involved in the auxin biosynthe sis pathway in transformed plant cells. The short divergent promoter r egion between the two aux-coding sequences contains the main regulator y elements. This region was fused to the uidA reporter gene and introd uced into Nicotiana tabacum in order to investigate the regulation and the tissue specificity of these genes. Neither wound nor hormone indu ction could be detected on transgenic leaf discs. However, phytohormon e concentration and auxin/cytokinin balance controlled the expression of the chimaeric genes in transgenic protoplasts. The expression was l ocalised in apical meristems, root tip meristems, lateral root primord ia, in cells derived from transgenic protoplasts and in transgenic cal li. Histological analysis showed that the expression was located in ce lls reactivated by in vitro culture. Experiments using cell-cycle inhi bitors such as hydroxyurea or aphidicolin on transgenic protoplast cul tures highly decreased the beta-glucuronidase activity of the chimaeri c genes. These results as well as the histological approach suggest a correlation between expression of the aux1 and aux2 genes and cell div ision.