A cysteine-rich secretory protein involves in phytohormone melatonin mediated plant resistance to CGMMV

Background: Melatonin is considered to be a polyfunctional master regulator in animals and higher plants. Exogenous melatonin inhibits plant infection by multiple diseases; however, the role of melatonin in cucumber green mottle mosaic virus (CGMMV) infection remains unknown. Results: In this study, we demonstrated that exogenous melatonin treatment can effectively control CGMMV infection. The greatest control effect was achieved by 3 days of root irrigation at a melatonin concentration of 50 µM. Exogenous melatonin showed preventive and therapeutic effects against CGMMV infection at early stage in tobacco and cucumber. We utilized RNA sequencing technology to compare the expression profiles of mock-inoculated, CGMMV-infected, and melatonin+CGMMV-infected tobacco leaves. Defense-related gene CRISP1 was specifically upregulated in response to melatonin, but not to salicylic acid (SA). Silencing CRISP1 enhanced the preventive effects of melatonin on CGMMV infection, but had no effect on CGMMV infection. We also found exogenous melatonin has preventive effects against another Tobamovirus, pepper mild mottle virus (PMMoV) infection. Conclusions: Together, these results indicate that exogenous melatonin controls two Tobamovirus infection and inhibition of CRISP1 enhanced melatonin control effects against CGMMV infection, which may lead to the development of a novel melatonin treatment for Tobamovirus control. N. benthamiana plants were irrigated daily with 50 µM melatonin for 3 days; ddH2O was used as a control. On day 4, CGMMV was inoculated onto plant leaves. Leaves were collected for RNA-Seq analysis at 9 dpi. Three replicate leaf samples were collected for each treatment (CGMMV_MEL, CGMMV_CK, and WT) and each sample contained leaves from at least eight plants. At 7 dpi with CGMMV, tobacco leaves were collected for total RNA extraction.