Physiological, Biochemical, and Transcriptome Analyses Reveal the Potential Role of ABA in Dufulin-Induced Tomato Resistance to Tomato Brown Rugose Fruit Virus (ToBRFV)

As an important plant immune inducer, Dufulin has long been thought to enhance plant resistance to multiple plant viruses through activating the salicylic acid (SA) pathway. However, whether this immune inducer responds to tomato brown rugose fruit virus (ToBRFV) infection in the same way remains uncertain. In this study, we systematically analyzed the multiple effects of Dufulin treatment on the physiological, biochemical and gene expression patterns in tomato under ToBRFV infection. The results showed that the application of Dufulin could significantly increase the chlorophyll content; elevate the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT); reduce the ToBRFV viral load; and enhance plant growth. Moreover, we found that Dufulin treatment could increase both SA and abscisic acid (ABA) contents. However, SA-related genes were not strongly activated as the genes involved in ABA biosynthesis and signal transduction pathways. This suggested that ABA likely plays an unrecognized role in the formation of this induced resistance. Through weighted gene co-expression network analysis (WGCNA) and cis-element analysis of the target gene promoters, we identified that SlABI5-like and SlWRKY4 might be the key potential transcription factor genes for Dufulin-induced tomato resistance to ToBRFV, and constructed their molecular regulatory network. We also conducted qRT-PCR assay to verify the gene expression patterns involved in this study. These findings potentially provide new insights into the mechanism of Dufulin-induced antiviral resistance, and enlarge important molecular targets for ToBRFV prevention and control.