A PEROXIDASE GENE PROMOTER INDUCED BY PHYTOPATHOGENS AND METHYL JASMONATE IN TRANSGENIC PLANTS

The expression of two closely related peroxidase isogenes, Shpx6a and Shpx6b, of the legume Stylosanthes humilis was studied using isogene-s pecific reverse transcriptase PCR techniques. Results indicated that t ranscripts of both genes were rapidly induced following inoculation wi th the fungal pathogen Colletotrichum gloeosporioides, wounding and tr eatment with the defense regulator methyl jasmonate (MeJA). In contras t, treatment of leaves of S. humilis with abscisic acid (ABA) and sali cylic acid (SA) did not induce transcripts of either isogene. A genomi c clone containing the Shpx6b gene was isolated and 594 bp of 5' seque nce upstream of the translation start was fused in frame to the coding region of the uidA reporter gene and introduced into tobacco. Express ion from the Shpx6b promoter in transgenic plants was determined by hi stochemical staining and quantitative assays of beta-glucuronidase (GU S). In transgenic tobacco, GUS expression was detected in cotyledons, vascular cells of young leaves, anthers, pollen, and the stigma and st yle. Wounding of the tobacco plants produced very localized GUS staini ng. Much more extensive staining for GUS was observed following inocul ation of tobacco leaves with conidia of the fungal pathogen Cercospora nicotianae and the inoculation of wound sites with mycelium of the Oo mycete pathogen Phytophthora parasitica var. nicotianae. Treatment of mature leaves with methyl jasmonate induced GUS activity while treatme nt with ABA, SA, and H2O2 had no effect. A similar strong induction of GUS activity was measured in young transgenic seedlings germinated on MeJA while some, but much weaker, induction of GUS activity was obser ved in seedlings treated with SA. The sequence of the promoter contain ed motifs homologous to putative cis elements in other plant genes res ponsive to MeJA. The Shpx6b gene is the first plant peroxidase gene sh own to be induced by both microbial pathogens and MeJA and its promote r will be useful for investigations of signaling processes during fung al infection and for the expression of foreign gene products at infect ion sites.