Transgenic silver birch (Betula pendula) expressing sugarbeet chitinase 4 shows enhanced resistance to Pyrenopeziza betulicola

A sugar beet chitinase gene driven by the (42) CaMV 35S promoter was introduced into silver birch (Betula pendula) through Agrobacterium-mediated transformation. Transgenic shoots were regenerated and grown on WPM medium supplemented with 150 mg/ml kanamycin. From a total of 220 explants, 52 transgenics were obtained and 13 transgenic lines were randomly taken for molecular analysis to confirm the presence of the introduced sugar beet chitinase 4 cDNA by polymerase chain reaction and Southern hybridisation. All 13 transgenic lines were confirmed to contain the gene and further characterised. Northern blot analysis of total RNA indicated that the transgenic lines differed with respect to the steady-state levels of chitinase mRNA. Transgenic lines with high levels of mRNA of chitinase 4 cDNA consistently showed higher levels of resistance to Pyrenopeziza betulicola than transgenics with intermediate or low mRNA levels or a non-transgenic control plant. This report demonstrates that the constitutive expression of this gene in transgenic birch lines increased the resistance of birch against the leaf spot fungus P. betulicola.