Knockdown of PHYTOENE DESATURASE in the field dodder, Cuscuta campestris, by Virus-Induced Gene Silencing

Cuscuta campestris is a globally distributed obligate holoparasitic plant, and economically important crop pest. There is an urgent need for safe and effective new herbicides to control Cuscuta spp. PHYTOENE DESATURASE (PDS) is a biosynthetic enzyme within the carotenoid synthesis pathway, which is a target for several commercially available herbicides. The low transpiration rate of C. campestris results in sub-optimal translocation of PDS-targeting herbicides throughout the parasite, and resistance to these herbicides, and others, should be anticipated. Here we demonstrate that RNA interference (RNAi) can effectively reduce the expression of PDS in C. campestris. Virus Induced Gene Silencing (VIGS) is capable of inducing PDS knockdown in C. campestris, when Tobacco Rattle Virus (TRV) is used to deliver a PDS-specific sequence through the host plant Arabidopsis thaliana. This leads to a reduction in the accumulation of beta carotene, which is synthesised from phytoene, and significantly reduced growth of C. campestris. We hypothesise that secondary amplification and spread of PDS double-stranded RNA within C. campestris may circumvent the translocation limitations of other xylem and phloem-spread PDS-specific herbicides. These data demonstrate for the first time that VIGS can be used for reverse genetics interrogation of the C. campestris genome.