Transcriptomics of host-specific interactions in natural populations of the parasitic plant purple witchweed (Striga hermonthica)

Authors: LOPES, LUA - Pennsylvania State University; BELLIS, EMILY - Pennsylvania State University; WAFULA, ERIC - Pennsylvania State University; HEARNE, SARAH - International Institute Of Tropical Agriculture (IITA); Honaas, Loren; RALPH, PAULA - Pennsylvania State University; UNACHUKWU, NNANNA - International Institute Of Tropical Agriculture (IITA); DEPAMPHILIS, CLAUDE - Pennsylvania State University; LASKY, JESSE - Pennsylvania State University

Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/13/2019
Publication Date: 6/10/2019
Citation: Lopes, L., Bellis, E., Wafula, E., Hearne, S., Honaas, L.A., Ralph, P., Unachukwu, N., dePamphilis, C., Lasky, J. 2019. Transcriptomics of host-specific interactions in natural populations of the parasitic plant purple witchweed (Striga hermonthica). Weed Science. 67(4):397-411. https://doi.org/10.1017/wsc.2019.20.
DOI: https://doi.org/10.1017/wsc.2019.20

Interpretive Summary: Plants have complex genomes that contain large multi-gene families with genes that are highly similar, but have specialized functions. In this paper, we used big data to link plant genes to plant traits. Understanding how these minor gene differences impact important plant functions, like plant-pathogen interactions, helps us understand how plants respond to their environment. Enhanced understanding of these plant responses helps us improve and better manage plants that are important for humans. Specifically, this work identifies particular gene forms that are important for plant-pathogen interactions long after initial contact, revealing additional opportunities for pathogen control.

Technical Abstract: Host-specific interactions can maintain genetic and phenotypic diversity in parasites that attack multiple host species. Host diversity may promote parasite diversity by selection for genetic divergence or plastic responses to host type. The parasitic weed Striga hermonthica causes devastating yield losses in sub-Saharan Africa and is capable of infesting a wide range of grass hosts. Despite some evidence for host adaptation and host-by-Striga genotype interactions, little is known about intraspecific Striga genomic diversity. Here we present the first study of transcriptomic diversity in above ground tissue populations of Striga hermonthica growing on different hosts. We explored host-associated variation in transcriptomes of this obligate hemiparasite analyzing pooled-RNAseq libraries from populations in Nigeria parasitizing maize and sorghum using gene expression and changes in allele frequency of expressed genes, in addition to evidence for selection on specific genes. Despite low levels of genome wide differentiation within and among populations, we identified a set of host-associated transcripts. In agreement with previous studies in several parasitic plants, we identified several functional genes categories relevant for host-parasite interaction. Namely, our results highlight the role that nutrients transporters interactions and aboveground organs have in host-specific interactions. Host-recognition is a multilevel process and those parasite’ss genotypes that are not removed by selection during germination and haustoria connection can be latter selected by the pressures that host, as an environment, have in the parasite (physiological integration at the vegetative stage). In addition, we found several defense and pathogenesis related genes together with plant hormone-response genes, supporting the idea that pathways involved in plant defense/pathogenesis and hormone-response can be used by the parasite during the parasitic process. Overall, we provide a set of candidate transcripts that show host-specific interactions in above ground tissue in the parasitic plant S. hermonthica. Our research shows how signals of host-specific processes can be detected aboveground, expanding the focus of host-parasite interactions beyond the haustoria connection.