LATERAL ORGAN BOUNDARIES DOMAIN 25 functions as a key regulator of haustorium development in dodders

Abstract

Parasitic plants reduce crop yield worldwide. Dodder (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, LATERAL ORGAN BOUNDARIES DOMAIN 25 (CcLBD25), as highly expressed in prehaustoria and haustoria. Gene co-expression networks (GCN) from different tissue types and laser-capture microdissection (LCM) RNA-Seq data indicated that CcLBD25 could be essential for regulating cell wall loosening and organogenesis. We employed host-induced gene silencing (HIGS) by generating transgenic tomato (Solanum lycopersicum) 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 reduced biomass compared with C. campestris growing on wild-type hosts, suggesting that parasites growing on transgenic plants were stressed due to insufficient nutrient acquisition. We developed an in vitro haustorium (IVH) system to assay the number of prehaustoria produced on strands from C. campestris. C. campestris grown on CcLBD25 RNAi tomatoes produced fewer prehaustoria than those grown on wild-type tomatoes, indicating that down-regulating CcLBD25 may affect haustorium initiation. C. campestris haustoria growing on CcLBD25 RNAi tomatoes exhibited reduced pectin digestion and lacked searching hyphae, which interfered with haustorium penetration and formation of vascular connections. The results of this study elucidate the role of CcLBD25 in haustorium development and might contribute to developing parasite-resistant crops.

Investigating Host and Parasitic Plant Interaction by Tissue-Specific Gene Analyses on Tomato and Cuscuta campestris Interface at Three Haustorial Developmental Stages

“…Using GO enrichment analysis, we noticed that the SOM3 module 2 has enriched biological process GO terms including “root radial pattern formation” ( Supplementary Table 5 ). This result matches our recent discovery that C. campestris also utilizes the root developmental program during haustorium organogenesis ( Jhu et al, 2021 ). Therefore, we focused on SOM3 module 2 for further analysis.…”

“…(B) , (D) , (E) , and (F) , scale bars = 100 μm. Part of this figure (A–C) is modified from one in a previously published paper Jhu et al, 2021 with new information added.…”

“…Last but not least, the previously identified key regulator in C. campestris haustorium development, transcription factor LATERAL ORGAN BOUNDARIES DOMAIN 25 ( CcLBD25 ) ( Jhu et al, 2021 ) is classified in SOM6, which is enriched with genes that are highly expressed in the early and mature haustorial stage ( Figure 2G ). The SOM6 GCN is composed of four major modules based on the GCN community structure ( Figure 2H and Supplementary Table 4 ).…”

“…For tomato genes, the current published tomato genome ITAG4.0 is well-annotated, so the gene name and functional annotation that is currently available on the Sol Genomics Network website ( https://solgenomics.net/ ) were used in this study. For C. campestris genes, since many genes are not functionally annotated in the current published C. campestris genome ( Vogel et al, 2018 ), we used our previously published master list for annotated C. campestris transcriptome ( Ranjan et al, 2014 ) combined with C. campestris genome gene IDs to create a more complete functional annotation ( Jhu et al, 2021 ). TAIR ID hits were used for GO Enrichment Analysis on http://geneontology.org/for gene clusters and modules.…”

“…The mature stage has two libraries. This figure is modified from one of the supplemental figures in our previously published paper Jhu et al (2021) .…”