SlARG2 contributes to MeJA-induced defense responses to Botrytis cinerea in tomato fruit

BACKGROUND Arginase plays key roles in methyl jasmonate (MeJA)-mediated quality maintenance in vegetables and fruits. MeJA treatment induced the Arginase 2 (SlARG2) expression, which is one of the most important encoding genes of arginase. In addition, the treatment with MeJA induced resistance to pathogenic infection in many plants. However, the functions of SlARG2 in MeJA-induced defense to Botrytis cinerea are unclear. In our work, control and SlARG2-silenced tomato fruits (Solanum lycopersicum) were treated with 0.05 mmoL L-1 MeJA before storage to assay the roles of SlARG2 in MeJA-induced defense responses to Botrytis cinerea. RESULTS Our results indicated that MeJA treatment induced both pathogenesis-related gene expression (PR1, PR2a, PR2b and PR3b), and the activity of defense-related enzymes, as well as upregulated arginine metabolism. Compared to control fruits, the treatment with MeJA also induced the activity of arginase, arginine decarboxylase (ADC) and ornithine aminotransferase (OAT), and expression of SlARG2, SlADC, ornithine decarboxylase (SlODC) and SlOAT, and consequently increased the accumulation of arginine, proline, glutamate, putrescine and spermine. However, the induction effects by MeJA were significantly reduced in fruits in which SlARG2 was silenced and severe disease symptoms were observed. CONCLUSION MeJA fumigation could inhibit disease development by inducing pathogenesis-related gene expression (PR1, PR2a, PR2b and PR3b) and defense-related enzymes activity, as well as upregulated arginine metabolism. In addition, SlARG2 silencing could inhibit the functions of MeJA in inducing the accumulation of the above substances. Overall, our study provided strong evidence that SlARG2 was essential for MeJA-induced tomato fruit defense responses to Botrytis cinerea.