Trichosanthes kirilowii: A New Host of Cucurbit mild mosaic virus in China

Molecular identification and development of an infectious cDNA clone of Trichosanthes kirilowii-infecting cucurbit mild mosaic virus

Trichosanthes kirilowii has been mainly grown for use in traditional Chinese medicine. In this study, cucurbit mild mosaic virus (CuMMV) belonging to the genus Fabavirus was identified from T. kirilowii plants. CuMMV possesses a segmented, bipartite linear single-stranded RNA genome composed of RNA1 and RNA2. Sequence analysis showed that each genomic segment shares the highest sequence similarity with those of CuMMV isolated from pumpkin. A full-length infectious cDNA clone of CuMMV was further constructed and was found to induce typical symptoms in T. kirilowii, Cucumis sativus, C. melo, Citrullus lanatus, and Cucurbita pepo. The sap inoculum derived from the infectious cDNA clone of CuMMV could be mechanically transmitted and reproduce similar symptoms in the tested plants. This is the first report on the construction of a biologically active, full-length infectious cDNA clone of CuMMV, which will provide a useful tool in understanding CuMMV-encoded proteins and plant-CuMMV interactions.

A Distinct Tobamovirus Associated With Trichosanthes kirilowii Mottle Mosaic Disease

Trichosanthes kirilowii is one of the most important perennial herbaceous vines that have been used in traditional Chinese medicine. In this study, a novel RNA virus was discovered in T. kirilowii plants showing leaf mottling and mosaic symptoms. The complete genome of this virus is 6,524 nucleotides long and encodes four open reading frames which are arranged in a manner typical of tobamoviruses. Phylogenetic analysis based on the complete genome sequence revealed that the virus was clustered into a branch with the tobamoviruses whose natural host are plants belonging to the family Cucurbitaceae. A full-length infectious cDNA clone was then constructed and demonstrated to establish a systemic infection with typical symptoms in Nicotiana benthamiana, T. kirilowii, and five other cucurbitaceous crops including Cucumis melo, C. lanatus, C. sativus, Luffa aegyptiaca, and Cucurbita pepo via agrobacterium-mediated infectivity assays. Further experiments provided evidence that the rod-shaped viral particles derived from the infectious clone could be mechanically transmitted and reproduce indistinguishable symptoms in the tested plants. Taken together, the mottle mosaic disease of T. kirilowii is caused by a distinct tobamovirus, for which the name Trichosanthes mottle mosaic virus (TrMMV) is proposed. As the infectious cDNA clone of TrMMV could also infect five other cucurbit crops, this distinct tobamovirus could be a potential threat to other cucurbitaceous crops.