GENETIC ENGINEERING OF REPRODUCTIVE STERILITY IN PINUS RADIATA

Abstract

Generation of transgenic trees for reproductive incompetence is an important application of genetic engineering to commercial forestry. This involves isolation and characterisation of the regulatory regions of the genes expressed at the very early stages of male and female reproductive organ development. A gene family showing specific expression in Pinus radiata immature male and female cone-buds was isolated and characterised. A cell ablation strategy involving expression of toxin genes, under the control of the regulatory sequences of these genes, led to the ablation of the target cells. The major problem with this strategy was 'promoter leakage', low (background) levels of expression of some flower-specific promoters in vegetative tissues during flowering and non-flowering periods. To improve the cell ablation strategy, a cascade of chimeric genes was designed. During non-flowering, controlled expression of the anti-toxin gene from Bacillus amyloliquefaciens, Barstar, in non-flowering tissues arrested the accumulation of the toxic Barnase protein.