ANALYSIS OF LATE-BLIGHT DISEASE RESISTANCE AND FREEZING TOLERANCE IN TRANSGENIC POTATO PLANTS EXPRESSING SENSE AND ANTISENSE GENES FOR AN OSMOTIN-LIKE PROTEIN

The expression patterns of plant defense genes encoding osmotin and os motin-like proteins imply a dual function in osmotic stress and plant pathogen defense. We have produced transgenic potato (Solanum commerso nii Dun.) plants constitutively expressing sense or antisense RNAs fro m chimeric gene constructs consisting of the cauliflower mosaic virus 35S promoter and a cDNA (pA13) for an osmotin-like protein. Transgenic potato plants expressing high levels of the pA13 osmotin-like protein showed an increased tolerance to the late-blight fungus Phytophthora infestans at various phases of infection, with a greater resistance at an early phase of fungal infection. There was a decrease in the accum ulation of osmotin-like mRNAs and proteins when antisense transformant s were challenged by fungal infection, although the antisense transfor mants did not exhibit any alterations in disease susceptibility. Expre ssion of pA13 sense and antisense RNAs had no effect on the developmen t of freezing tolerance in transgenic plants when assayed under a vari ety of conditions including treatments with abscisic acid or low tempe rature. These results provide evidence of antifungal activity for a po tato osmotin-like protein against the fungus P. infestans, but do not indicate that pA13 osmotin-like protein is a major determinant of free zing tolerance.