Infection, replication, and expression of plant viruses in filamentous fungi

The recent demonstration that the plant virus tobacco mosaic virus replicates and expresses in the plant pathogenic fungus Colletotrichum spp. provides opportunities for examining fundamental aspects of the biology of plant pathogenic fungi and of their interaction with the host. The small genome size and the ability in colonizing systemically the host have implemented the use of plant viruses to carry segments of host genes that can then promote the silencing of the RNAs expressed from the corresponding endogenous genes in a process called virus-induced gene silencing (VIGS). This chapter presents support for the view that VIGS with a direct transfection of a plant virus vector in fungal cells can be used for functional genomics also in fungi that activate an antiviral defense based on RNA interference (RNAi). The silencing of genes in filamentous fungi is technically more problematic and labor intensive than in plants, especially if transgenic plants need to be generated first. Compared to current strategies to employ RNAi to investigate the basis of fungal pathogenesis, the VIGS approach described here is more direct, easy to do, and feasible. Future perspectives of both basic and practical aspects of this technology are discussed.