Stem rust resistance in wheat is suppressed by a subunit of the mediator complex

Authors: HIEBERT, COLIN - Agriculture And Agri-Food Canada; MOSCOU, MATTHEW - Sainsbury Laboratory; HEWITT, TIMOTHY - University Of Sydney; STEUERNAGEL, BURKHARD - John Innes Center; HERNANDEZ-PINZON, INMACULADA - Sainsbury Laboratory; GREEN, PHON - Sainsbury Laboratory; PUJOL, VINCENT - The Australian National University; ZHANG, PENG - University Of Sydney; Rouse, Matthew - Matt; Jin, Yue; MCINTOSH, ROBERT - University Of Sydney; UPADHYAYA, NARAYANA - Commonwealth Scientific And Industrial Research Organisation (CSIRO); ZHANG, JIANPING - Commonwealth Scientific And Industrial Research Organisation (CSIRO); BHAVANI, SRIDHAR - International Maize & Wheat Improvement Center (CIMMYT); VRANA, JAN - Institute Of Experimental Botany; KARAFIATOVA, MIROSLAVA - Institute Of Experimental Botany; HUANG, LI - Montana State University; FETCH, THOMAS - Agriculture And Agri-Food Canada; DOLEZEL, JAROSLAV - Institute Of Experimental Botany; WULFF, BRANDE - John Innes Center; LAGUDAH, EVANS - Commonwealth Scientific And Industrial Research Organisation (CSIRO); SPIELMEYER, WOLFGANG - Commonwealth Scientific And Industrial Research Organisation (CSIRO)

Submitted to: Nature Communications
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/11/2020
Publication Date: 2/28/2020
Citation: Hiebert, C.W., Moscou, M.J., Hewitt, T., Steuernagel, B., Hernandez-Pinzon, I., Green, P., Pujol, V., Zhang, P., Rouse, M.N., Jin, Y., McIntosh, R.A., Upadhyaya, N.M., Zhang, J., Bhavani, S., Vrana, J., Karafiatova, M., Huang, L., Fetch, T.G., Dolezel, J., Wulff, B.B., Lagudah, E.S., Spielmeyer, W. 2020. Stem rust resistance in wheat is suppressed by a subunit of the mediator complex. Nature Communications. 11(1123). https://doi.org/10.1038/s41467-020-14937-2.
DOI: https://doi.org/10.1038/s41467-020-14937-2

Interpretive Summary: Stem rust (Puccinia graminis f. sp. tritici) is an important fungal disease of wheat that can be controlled by developing cultivars that carry effective resistance genes. The wild-type form of gene SuSr-D1 identified in the cultivar 'Canthatch' suppresses stem rust resistance. SuSr-D1 mutants are resistant to several races of the stem rust fungus that are virulent on wild-type plants. Sequencing flow-sorted chromosomes from wild-type and mutant lines facilitated the isolation of SuSr-D1 through linkage and physical mapping. The gene was predicted to encode Med15, a subunit of the Mediator Complex, a conserved protein complex that regulates the expression of protein-coding genes in eukaryotes. Seven independent nonsense mutations in Med15b.D resulted in the expression of race-specific stem rust resistance. Suppression is a common phenomenon when transferring resistance genes from progenitor species to wheat and limits the reservoir of resistance genes available for sustainable wheat improvement. This study provides novel insight into suppression of rust resistance in wheat. The mutants of the suppressor gene could be used to breed wheat cultivars with improved resistance to stem rust. Resistant wheat cultivars protect U.S. wheat production from the threat of foreign virulent races of the stem rust pathogen.

Technical Abstract: Stem rust (Puccinia graminis f. sp. tritici) is an important fungal disease of wheat that can be controlled by developing cultivars that carry effective resistance genes. The wild-type form of gene SuSr-D1 identified in the cultivar 'Canthatch' suppresses stem rust resistance. SuSr-D1 mutants are resistant to several races of the stem rust fungus that are virulent on wild-type plants. Sequencing flow-sorted chromosomes from wild-type and mutant lines identified EMS-induced SNVs that facilitated the isolation of SuSr-D1 through linkage and physical mapping. The gene was predicted to encode Med15, a subunit of the Mediator Complex, a conserved protein complex that regulates the expression of protein-coding genes in eukaryotes. Seven independent nonsense mutations in Med15b.D resulted in the expression of race-specific stem rust resistance. Time-course RNAseq analysis found a significant reduction or complete loss of differential gene expression at 24 hours post inoculation in med15b.D mutants, suggesting that transcriptional reprogramming at this time point is not required for immunity to stem rust. Suppression is a common phenomenon when transferring resistance genes from progenitor species to wheat and limits the reservoir of resistance genes available for sustainable wheat improvement. This study provides novel insight into suppression of rust resistance in wheat.