Activation of two osmotin-like protein genes by abiotic stimuli and fungal pathogen in transgenic potato plants.

Osmotin-like proteins are encoded by at least six members of a multigene family in Solanum commersonii. A genomic clone (lambda pGEM2a-7) that contains two osmotin-like protein genes (OSML13 and OSML81) arranged in the same transcriptional orientation has been isolated. Restriction mapping and sequence analysis indicated that the two intronless genes correspond to the previously characterized pA13 and pA81 cDNAs. To study the transcriptional activation of OSML13 and OSML81 promoters, the 5' flanking DNA sequence (-1078 to +35 of OSML13 and -1054 to +41 of OSML81) was fused to the beta-glucoronidase (GUS) coding region, and the chimeric gene fusions were introduced into wild potato (S. commersonii) plants via Agrobacterium-mediated transformation. Analysis of the chimeric gene expression in transgenic potato plants showed that both 5' flanking DNA sequences are sufficient to impart GUS inducibility by abscisic acid, NaCl, salicylic acid, wounding, and fungal infection. Low temperature activated both chimeric genes only slightly. Infection with Phytophthora infestans resulted in strong GUS expression from both chimeric genes primarily in the sites of pathogen invasion, suggesting a limited diffusion of fungal infection-mediated signals. The expression patterns of both osmotin-like protein genes implicate their dual functions in osmotic stress and plant pathogen defense.