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.

Plants under stress by parasitic plants.

In addition to other biotic stresses, parasitic plants pose an additional threat to plants and cause crop losses, worldwide. Plant parasites directly connect to the vasculature of host plants thereby stealing water, nutrients, and carbohydrates consequently leading to tremendously reduced biomass and losses in seed yields of the infected host plants. Initial steps to understand the molecular resistance mechanisms and the successes in ancient and recent breeding efforts will provide fundamental knowledge to further generate crop plants that will resist attacks by plant parasites.

Growth Assay for the Stem Parasitic Plants of the Genus Cuscuta.

Cuscuta spp. are widespread obligate holoparasitic plants with a broad host spectrum. Rootless Cuscuta penetrates host stems with so called haustoria to form a direct connection to the host vascular tissue ( Dawson et al., 1994 ; Lanini and Kogan, 2005; Kaiser et al., 2015 ). This connection allows a steady uptake of water, assimilates and essential nutrients from the host plant and therefore enables Cuscuta growth and proliferation. To quantify the parasites' ability to grow on potential host plants one can use the quantitative growth assay ( Hegenauer et al., 2016 ) described herein, which exclusively utilizes fresh weight measurement as readout.

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 that 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. 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.

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.