Arbuscular Mycorrhizal Fungi Trigger Transcriptional Expression of Flavonoid and Chlorogenic Acid Biosynthetic Pathways Genes in Tomato against Tomato Mosaic Virus

Tomato mosaic disease, caused by Tomato Mosaic Virus (ToMV), is one of the most destructive diseases which results in serious crop losses. Research investigations dealing with the biocontrol activity of arbuscular mycorrhizal fungi (AMF) against this viral disease are limited. In this study, the biocontrol activity of AMF on tomato plants infected with ToMV was evaluated in the greenhouse. In addition, their impacts on the transcriptional expression levels of thirteen genes controlling the phenylpropanoid, flavonoid and chlorogenic acid biosynthetic pathways were also investigated using quantitative real-time PCR. Transcriptional expressions of the majority of the studied genes were up-regulated by mycorrhizal colonization in the presence of ToMV, particularly PAL1 and HOT, suggesting their pathogen-dependent inducing effect. Under greenhouse conditions, a significant reduction in the disease severity and incidence, as well as the viral accumulation level was observed as a response to the mycorrhizal colonization of the infected plants. Moreover, the evaluated growth parameters, photosynthetic pigments, and flavonoid content were significantly enhanced by AMF colonization. The obtained results demonstrated the protective role of AMF in triggering the plant immunity against ToMV in a pathogen-dependent manner. Beside their protective and growth-promotion activities, AMF are characterized by low-cost and environment-friendly properties which support their possible use for control of tomato mosaic disease.