SHR4z, a novel decoy effector from the haustorium of the parasitic weed Striga gesnerioides, suppresses host plant immunity

Authors: SU, CHUUN - University Of Virginia; LUI, HAI - University Of Virginia; WAFULA, ERIC - Pennsylvania State University; Honaas, Loren; DEPAMPHILIS, CLAUDE - Pennsylvania State University; TIMDO, MICHAEL - University Of Virginia

Submitted to: New Phytologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/22/2019
Publication Date: 12/1/2019
Citation: Su, C., Lui, H., Wafula, E., Honaas, L.A., dePamphilis, C., Timdo, M. 2019. SHR4z, a novel decoy effector from the haustorium of the parasitic weed Striga gesnerioides, suppresses host plant immunity. New Phytologist. 226:641-643. https://doi.org/10.1111/nph.16351.
DOI: https://doi.org/10.1111/nph.16351

Interpretive Summary: We compared massive gene activity data sets (i.e. big data) from two genetically similar, but distinct plants. We found a small number of genes that had different activity signatures - which is what we expect because these two plants are only slightly genetically different. But because these plants have distinct traits, we reasoned that among this short list of genes there might be genes that explain the trait differences between the closely related plants. After carefully screening these genes, and then following up with more experiments on the genes we thought were the best candidates to explain the trait differences, we found a single gene that seems to explain a major trait difference. This approach for identifying genes related to plant traits, called gene discovery, is a useful approach to link genes to a wide variety of plant traits. This is particularly relevant for plants with traits that are desirable for human uses, like pathogen resistance or fruit quality.

Technical Abstract: Cowpea (Vigna unguiculata L.) is the most important food and forage legume in the African Sahel providing essential protein nutrition and income to millions of farmers. While most cowpea cultivars are susceptible to the root parasitic weed Striga gesnerioides, cultivar B301 is resistant to all known parasite races except SG4z. When challenged by races SG4 and SG3, the roots of B301 display a hypersensitive response (HR) at the site of parasite attachment followed by death of the invading parasite. In contrast, no visible response occurs in B301 roots parasitized by SG4z and the parasite successfully penetrates the host root cortex, forms vascular connections, and grows to maturity. Comparative transcriptomics and in silico computational analysis uncovered a leucine-rich receptor (LRR)-protein kinase (PK) homolog dubbed SHR4z (Suppressor of Host Resistance 4z) that is highly expressed in SG4z haustoria and secreted into the host root. Overexpression of SHR4z in transgenic B301 roots leads to suppression of HR elicitation and loss of host innate immunity. SHR4z binds a host BTB-BACK domain containing ubiquitin E3 ligase homolog (VuPOB1) and silencing of VuPOB1 expression in transgenic B301 roots lowers the frequency of HR and increases the levels of successful parasitism by SG4. In contrast, overexpression of VuPOB1 results in decreased parasitism by SG4z suggesting VuPOB1 functions as a positive regulator of HR and plant innate immunity. These findings provide new insights into how parasitic weeds overcome host defenses and could potentially contribute to the development of novel strategies for controlling Striga and other parasitic weeds thereby enhancing crop productivity and food security globally.