IDENTIFICATION OF CIS-ACTING ELEMENTS INVOLVED IN THE REGULATION OF THE PATHOGENESIS-RELATED GENE STH-2 IN POTATO

We have characterized a genomic clone containing the potato pathogenes is-related genes STH-2 and STH-21. The two genes are found 4 kb apart on the same chromosome and their sequences are highly similar. They pr esent the same transcriptional orientation and are both interrupted by a single intron. A chimaeric gene consisting of 1015 bp of 5'-flankin g sequence and part of the first exon of STH-2 fused to the bacterial beta-glucuronidase gene was highly-expressed in tubers of transgenic p otato plants after wounding and elicitor treatments. The levels of act ivity observed in these transgenic plants parallel those observed for the accumulation of STH-2 mRNAs under similar conditions. This indicat es that cis-acting elements necessary for the proper activation of the gene are present within 1 kb of 5'-flanking sequences. Functional ana lysis of 5' deletions of the STH-2/GUS constructs by transient express ion in leaf protoplasts revealed the presence of an upstream regulator y sequence between -135 and -52 which contains a TGAC motif, and a pos sible negative regulatory region between -52 and -28. A factor present in nuclear extracts of wounded potato tubers was found to bind specif ically to nucleotides located between -135 to -105, suggesting that th is region contains important cis-regulatory elements.