GENETIC-TRANSFORMATION OF POPULUS GENOTYPES WITH DIFFERENT CHIMERIC GENE CONSTRUCTS - TRANSFORMATION EFFICIENCY AND MOLECULAR ANALYSIS

Aspen (Populus tremula) and hybrid aspen (P. tremula x P. tremuloides) were transformed with different gene constructs using two types of pr omoter. The aim was to determine the influence of the reporter gene ro lC, controlled by promoters of viral or plant origin, on genetic and m orphologic expression of different transgenic aspen clones. An improve d transformation method using leaf discs was developed by which putati ve transgenic plantlets were regenerated at high efficiencies (up to 3 4%) on kanamycin-containing medium. Transgenic aspen carrying the rolC gene from Agrobacterium rhizogenes under control of the cauliflower-3 5S-promoter are reduced in size with smaller leaves, whereas aspen tra nsgenic for the same rolC gene, but under control of the light inducib le rbcS promoter from potato, are only slightly reduced in size compar ed to untransformed controls. However, all clones carrying 35S-rolC an d rbcS-rolC genes revealed light-green colouration of leaves when comp ared to untransformed aspen. Owing to this special feature, constructs were used in which expression of the rolC gene was inhibited by inser tion of a transposable element, Ac, from maize. Transgenic aspen trans formed with the 35S-Ac-rolC and rbcS-Ac-rolC genes were morphologicall y similar to untransformed aspen, but out of 54 independently regenera ted 35S-Ac-rolC transgenic aspen clones, 30 clones showed light-green/ dark green variegated leaves. In contrast, out of 19 independently tra nsformed rbcS-Ac-rolC aspen clones, only two clones revealed light-gre en/dark green variegated leaves. The role of bacterial strains in tran sformation, and molecular genetics of transgenic aspen plants (includi ng the function of the transposable element, Ac, in the aspen genome) are discussed.