Antagonistic Effect of Salicylic Acid and Jasmonic Acid on the Expression of Pathogenesis-Related (PR) Protein Genes in Wounded Mature Tobacco Leaves

Abstract

Salicylic acid (SA) and jasmonic acid (JA) are essential compounds in the pathogen- and wound-signaling path­ ways accompanying induced expression of acidic and basic pathogenesis-related (PR) protein genes, respectively. How­ ever, on the effect of exogenously supplied SA and JA in in­ duction of PR gene expression, conflicting results have been obtained using various plant materials at different de­ velopmental stages. There is no clear evidence on these effects in the presence of both signals at the same time. We analyzed the effect of SA on wound- and JA-induced basic PR gene expression and that of JA on SA-induced acidic PR gene expression in mature tobacco leaves. Wound-in­ duced accumulation of transcripts for all 4 basic PR genes tested was enhanced in the presence of MeJA, and in­ hibited in the presence of SA. On the other hand, expres­ sion of all 3 acidic PR genes tested was induced by SA and was inhibited by MeJA. Using antibodies raised against acidic PR-l and PR-2 proteins, these effects were confirm­ ed at the protein level. These results indicated that JA works as an inducer of basic PR genes, and also as an inhib­ itor for acidic PR genes, while SA does the opposite.