Jasmonate and salicylate induce the expression of pathogenesis-related-protein genes and increase resistance to chilling injury in tomato fruit

Treatment of tomato (Lycopersicon esculentum L. cv. Beefstake) fruit with low concentrations of (0.01 mM) methyl jasmonate (MeJA) or methyl salicylate (MeSA) substantially enhanced their resistance to chilling temperature and decreased the incidence of decay during low-temperature storage. While studying the expression of pathogenesis-related (PR) protein genes, different accumulation patterns of PR-protein mRNAs in tomato fruit were observed. MeJA substantially increased the accumulation of PR-2b transcripts encoding intracellular β-1,3-glucanase and enhanced the mRNA levels of PR-2a and PR-3b encoding extracellular β-1,3-glucanase and intracellular chitinase, respectively. MeSA substantially increased accumulation of PR-2b and PR-3a mRNAs and slightly increased PR-3b mRNA accumulation. Chilling temperature did not appreciably enhance the accumulation of PR-protein mRNAs in untreated fruit. However, the accumulation of PR-3b mRNAs in MeSA-treated fruit was enhanced following low-temperature storage. Transcript abundance of catalase genes also was investigated in different pretreated tomatoes. The accumulation of cat1 mRNA was increased substantially by MeJA, while it was reduced by MeSA treatment. These results suggest that the pre-treatment of tomato fruit with MeSA or MeJA induces the synthesis of some stress proteins, such as PR proteins, which leads to increased chilling tolerance and resistance to pathogens, thereby decreasing the incidence of decay.