CcLBD25functions as a key regulator of haustorium development inCuscuta campestris

Abstract

Parasitic plants reduce yield of crops worldwide. Cuscuta campestris is a stem parasite that attaches to its host, using haustoria to extract nutrients and water. We analyzed the transcriptome of six C. campestris tissues 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 that CcLBD25 could 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-regulate CcLBD25 in the parasite. Our results showed that C. campestris growing on CcLBD25 RNAi transgenic tomatoes transited to the flowering stage earlier and had less biomass compared with C. campestris growing on wild type host. This suggests that the parasites growing on the transgenic plants were stressed due to insufficient nutrient acquisition. Anatomy of C. campestris haustoria growing on CcLBD25 RNAi tomatoes showed reduced pectin digestion and lack of searching hyphae, which interfered with haustorium penetration and the formation of vascular connections. We developed an in vitro haustorium (IVH) system to assay the number of prehaustoria produced on strands from C. campestris. When C. campestris was grown on CcLBD25 RNAi tomatoes or wild type tomatoes, the former produce fewer prehaustoria than the latter, indicating that down-regulating CcLBD25 may affect haustorium initiation. The results of this study shed light on the role of CcLBD25 in haustorium development and might help to develop a parasite-resistant system in crops.One-sentence summaryCcLBD25 plays a pivotal role in haustorium initiation, regulating pectin digestion, and searching hyphae development during the haustorium penetration process.

Gene regulatory networks for compatible versus incompatible grafts identify a role for SlWOX4 during junction formation

“…We designed our study to investigate the involvement of wound-induced tissue regeneration during junction formation, and thus this work inherently uncovers genetic hubs that were not previously considered to play a role in grafting. These hubs have, however, been implicated in the related process of haustorium formation in parasitic plants, and thus provide molecular support for the connection between graft junctions and haustoria ( Melnyk et al, 2018 ; Xie et al, 2019 ; Jhu et al, 2021 ). The fact that we identified diverse regulatory hubs between our species, supports a model in which grafting is not controlled by genetically conserved regulatory genes that are evolutionarily programmed into plant genomes.…”

Cuscuta species: Model organisms for haustorium development in stem holoparasitic plants

“…The genomes of C. campestris and C. australis were both published in 2018 (Sun et al, 2018;Vogel et al, 2018). The Cuscuta transcriptome profiles in different developmental stages and tissue types are readily available (Ranjan et al, 2014;Jhu et al, 2021;Bawin et al, 2022). Cuscuta mobile mRNAs and miRNAs that can transfer into the host plants are also reported (Kim et al, 2014;Shahid et al, 2018).…”

“…In addition, as mentioned in previous sections, many studies have shown that far-red light signals and physical contacts can trigger Cuscuta haustorium formation (Furuhashi et al, 1995;Tada et al, 1996;Furuhashi et al, 1997;Haidar and Orr, 1999). Therefore, several in vitro methods of growing Cuscuta or inducing haustorium formation without hosts have also been developed simultaneously (Kaga et al, 2020;Jhu et al, 2021;Bernal-Galeano et al, 2022). These methods allow us to investigate the function of genes in haustorium organogenesis more effectively and remove the influence or variations created by host conditions.…”

“…Based on previous studies, Cuscuta haustoria not only transport water and nutrients but also can transport small RNAs, messenger RNAs and small peptides (Kim et al, 2014;Kim and Westwood, 2015;Shahid et al, 2018;Wu, 2018;Johnson and Axtell, 2019). Therefore, host-induced gene silencing (HIGS) is a commonly used method to knock-down specific gene expressions in Cuscuta by attaching them to transgenic hosts that carry RNA interference (RNAi) constructs targeting Cuscuta genes (Albert et al, 2006;Alakonya et al, 2012;Jhu et al, 2021;. This method has been used widely in the Cuscuta research field to conduct functional analysis on genes of interest.…”