Perception of the parasitic plant Cuscuta reflexa, as an invader, by the tomato Solanum lycopersicum.

Cuscuta spp. are assigned to the family of the Morning glories (Convolvulaceae) and live as obligate holoparasitic plants, which infect the shoot of the host plants. They have a broad host spectrum and infect nearly all dicot plants with a few notable exceptions. For example, tomato (Solanum lycopersicum) is able to fend off the parasite’s attack with an active defense. It responds to extracts of C. reflexa in a similar manner as known for the detection of microbe-associated molecular patterns (MAMPs) (e.g. increased ethylene biosynthesis and the production of reactive oxygen species (ROS)). Using recombinant inbred lines between the resistant S. lycopersicum and the susceptible S. pennellii allowed for mapping of the corresponding locus within the tomato genome, responsible for the response against Cuscuta. Further mapping led to the identification of the leucine-rich repeat receptor like protein (LRR-RLP) CuRe1 (Cuscuta Receptor 1). CuRe1 perceives a molecular pattern from C. reflexa and subsequently induces the defense responses described above. Initial characterization indicated for a proteinaceous defense trigger with potential secondary modifications. To identify this parasite associated molecular pattern (ParAMP) we used chromatographic purification techniques (SPE, FPLC, HPLC) and mass spectrometry (MS). After purification and subsequent analyses, we found multiple 2-3 kDa peptides in different fractions of the C. reflexa extract that could be correlated with the CuRe1 activation. After in-depth MS analyses and partial peptide sequencing, we found that these peptides are degradation products of the same precursor protein, a class II C. reflexa glycine-rich protein (CrGRP). We could specify the epitope within the protein to a 21 aa long peptide with six cysteine residues. Synthesized peptides as well as heterologously expressed CrGRP were able to induce CuRe1-dependent defense responses. These findings demonstrate CrGRP as the ParAMP which is specifically recognized by CuRe1 and enables tomato to detect C. reflexa as a pathogenic invader. Notably, GRPs are widespread among plants, microbes and animals. Tomato itself possesses this type of GRP with a comparable six Cysteine motif. Nevertheless, these tomato homologs do not activate CuRe1. Future work will address the question why this motif serves as a specific target for Cuscuta perception

The tomato receptor CuRe1 senses a cell wall protein to identify Cuscuta as a pathogen

Parasitic plants of the genus Cuscuta penetrate shoots of host plants with haustoria and build a connection to the host vasculature to exhaust water, solutes and carbohydrates. Such infections usually stay unrecognized by the host and lead to harmful host plant damage. Here, we show a molecular mechanism of how plants can sense parasitic Cuscuta. We isolated an 11 kDa protein of the parasite cell wall and identified it as a glycine-rich protein (GRP). This GRP, as well as its minimal peptide epitope Crip21, serve as a pathogen-associated molecular pattern and specifically bind and activate a membrane-bound immune receptor of tomato, the Cuscuta Receptor 1 (CuRe1), leading to defense responses in resistant hosts. These findings provide the initial steps to understand the resistance mechanisms against parasitic plants and further offer great potential for protecting crops by engineering resistance against parasitic plants

Parasitic Cuscuta factor(s) and the detection by tomato initiates plant defense

Dodders (Cuscuta spp.) are holoparasitic plants that enwind stems of host plants and penetrate those by haustoria to connect to the vascular bundles. Having a broad host plant spectrum, Cuscuta spp infect nearly all dicot plants – only cultivated tomato as one exception is mounting an active defense specifically against C. reflexa. In a recent work we identified a pattern recognition receptor of tomato, “Cuscuta Receptor 1“ (CuRe1), which is critical to detect a “Cuscuta factor” (CuF) and initiate defense responses such as the production of ethylene or the generation of reactive oxygen species. CuRe1 also contributes to the tomato resistance against C. reflexa. Here we point to the fact that CuRe1 is not the only relevant component for full tomato resistance but it requires additional defense mechanisms, or receptors, respectively, to totally fend off the parasite

Detection of the plant parasite Cuscuta reflexa by a tomato cell surface receptor

Parasitic plants are a constraint on agriculture worldwide. Cuscuta reflexa is a stem holoparasite, which infests most dicotyledonous plants. One exception is tomato, which is resistant to C. reflexa. We discovered that tomato responds to a small peptide factor occurring in Cuscuta spp. with immune responses typically activated after perception of microbe-associated molecular patterns (MAMPs). We identified the cell surface receptor-like protein CUSCUTA RECEPTOR 1 (CuRe1) as essential for the perception of this parasite-associated molecular pattern. CuRe1 is sufficient to confer responsiveness to the Cuscuta factor and increased resistance to parasitic C. reflexa when heterologously expressed in otherwise susceptible host plants. Our findings reveal that plants recognize parasitic plants in a manner similar to perception of microbial pathogens, with potential for engineering resistance to parasitic plants in crops

The tomato receptor CuRe1 senses a cell wall protein to identify Cuscuta as a pathogen

Parasitic plants of the genus Cuscuta penetrate shoots of host plants with haustoria and build a connection to the host vasculature to exhaust water, solutes and carbohydrates. Such infections usually stay unrecognized by the host and lead to harmful host plant damage. Here, we show a molecular mechanism of how plants can sense parasitic Cuscuta. We isolated an 11 kDa protein of the parasite cell wall and identified it as a glycine-rich protein (GRP). This GRP, as well as its minimal peptide epitope Crip21, serve as a pathogen-associated molecular pattern and specifically bind and activate a membrane-bound immune receptor of tomato, the Cuscuta Receptor 1 (CuRe1), leading to defense responses in resistant hosts. These findings provide the initial steps to understand the resistance mechanisms against parasitic plants and further offer great potential for protecting crops by engineering resistance against parasitic plants