CcLBD25functions as a key regulator of haustorium development inCuscuta campestris

Parasitic plants reduce yield of crops worldwide.Cuscuta campestrisis a stem parasite that attaches to its host, using haustoria to extract nutrients and water. We analyzed the transcriptome of sixC. campestristissues and identified a key gene,CcLBD25, as highly expressed in prehaustoria and haustoria. Our gene co-expression networks (GCN) from different tissue types and laser-capture microdissection (LCM) RNA-Seq data indicate thatCcLBD25could be essential for regulating cell wall loosening and organogenesis. We employed host-induced gene silencing (HIGS) by generating transgenic tomato hosts that express hairpin RNAs to target and down-regulateCcLBD25in the parasite. Our results showed thatC. campestrisgrowing onCcLBD25RNAi transgenic tomatoes transited to the flowering stage earlier and had less biomass compared withC. campestrisgrowing on wild type host. This suggests that the parasites growing on the transgenic plants were stressed due to insufficient nutrient acquisition. Anatomy ofC. campestrishaustoria growing onCcLBD25RNAi tomatoes showed reduced pectin digestion and lack of searching hyphae, which interfered with haustorium penetration and the formation of vascular connections. We developed anin vitrohaustorium (IVH) system to assay the number of prehaustoria produced on strands fromC. campestris. WhenC. campestriswas grown onCcLBD25RNAi tomatoes or wild type tomatoes, the former produce fewer prehaustoria than the latter, indicating that down-regulatingCcLBD25may affect haustorium initiation. The results of this study shed light on the role ofCcLBD25in haustorium development and might help to develop a parasite-resistant system in crops.One-sentence summaryCcLBD25plays a pivotal role in haustorium initiation, regulating pectin digestion, and searching hyphae development during the haustorium penetration process.