PROTEIN DISULFIDE ISOMERASE LIKE 5-1 Is a Susceptibility Factor to Plant Viruses
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PROTEIN DISULFIDE ISOMERASE LIKE 5-1 is a susceptibility factor to plant viruses Ping Yanga, Thomas Lüpkenb, Antje Habekussb, Goetz Henselc, Burkhard Steuernageld,1, Benjamin Kiliana, Ruvini Ariyadasaa, Axel Himmelbacha, Jochen Kumlehnc, Uwe Scholzd, Frank Ordonb,2, and Nils Steina,2,3 aGenome Diversity, Department Genebank, Leibniz Institute of Plant Genetics and Crop Plant Research, D-06466 Gatersleben, Germany; bInstitute for Resistance Research and Stress Tolerance, Julius Kuehn Institute, Federal Research Centre for Cultivated Plants, D-06484 Quedlinburg, Germany; cPlant Reproductive Biology, Department of Physiology and Cell Biology, Leibniz Institute of Plant Genetics and Crop Plant Research, D-06466 Gatersleben, Germany; and dBioinformatics and Information Technology, Department of Cytogenetics and Genome Analyses, Leibniz Institute of Plant Genetics and Crop Plant Research, D-06466 Gatersleben, Germany Edited by David C. Baulcombe, University of Cambridge, Cambridge, United Kingdom, and approved January 3, 2014 (received for review October 29, 2013) Protein disulfide isomerases (PDIs) catalyze the correct folding of (10, 11). In addition, to establish replication and assembly com- proteins and prevent the aggregation of unfolded or partially plexes during infection, viruses typically create membrane-bound folded precursors. Whereas suppression of members of the PDI environments, referred to as “virus factories” (12). There, cellular gene family can delay replication of several human and animal chaperones such as HSP70 and DNAJ-like proteins likely contrib- viruses (e.g., HIV), their role in interactions with plant viruses is ute to the correct folding and translocation of substrates (12, 13). largely unknown. Here, using a positional cloning strategy we However, only a few such host factors are known (7, 9, 14). identified variants of PROTEIN DISULFIDE ISOMERASE LIKE 5–1 Barley yellow mosaic virus disease caused by barley yellow (HvPDIL5-1) as the cause of naturally occurring resistance to mul- mosaic virus (BaYMV) and barley mild mosaic virus (BaMMV) tiple strains of Bymoviruses. The role of wild-type HvPDIL5-1 in (both belong to Bymoviruses) seriously threatens winter barley conferring susceptibility was confirmed by targeting induced local production in Europe and East Asia (4). Infection leads to yel- lesions in genomes for induced mutant alleles, transgene-induced low discoloration and stunted growth and may result in yield loss complementation, and allelism tests using different natural resis- of up to 50% (15). Soil-borne transmission via the plasmodio- tance alleles. The geographical distribution of natural genetic var- phorid Polymyxa graminis prohibits plant protection by chemical iants of HvPDIL5-1 revealed the origin of resistance conferring measures, and breeding for resistant cultivars is therefore the alleles in domesticated barley in Eastern Asia. Higher sequence only practicable way to prevent yield loss. The naturally occur- ring recessive resistance locus rym11 confers complete broad- diversity was correlated with areas with increased pathogen di- spectrum resistance to all known European isolates of BaMMV versity suggesting adaptive selection for bymovirus resistance. and BaYMV (16–19). In the present study, we used a positional HvPDIL5-1 homologs are highly conserved across species of the cloning strategy to identify the gene underlying rym11-based re- plant and animal kingdoms implying that orthologs of HvPDIL5-1 PDI sistance. We show that it is a susceptibility factor belonging to or other closely related members of the gene family may be a gene family of PROTEIN DISULFIDE ISOMERASES (PDIs), potential susceptibility factors to viruses in other eukaryotic species. and is highly conserved across eukaryotic species. We observe a strong correlation between natural allelic variation and geographic allele mining | resistance breeding | soil-borne virus disease | chaperone distribution, suggesting that both the origin and subsequent nfectious diseases caused by plant viruses threaten agricultural Significance Iproductivity and reduce globally attainable agricultural pro- duction by about 3% (1). In specific pathosystems, plant viruses This work describes a susceptibility factor to plant viruses that can result in the loss of the entire crop. For example, the dev- belongs to the conserved PROTEIN DISULFIDE ISOMERASE (PDI) astation of cassava production by cassava mosaic geminiviruses gene family. We show that loss-of-function HvPDIL5-1 alleles (CMGs) in Uganda during the 1990s led to widespread food at the recessive RESISTANCE TO YELLOW MOSAIC DISEASE 11 shortages and famine-related deaths (2). Unfortunately pro- (rym11) resistance locus confer broad-spectrum resistance to tecting plants against viruses (especially soil-borne viruses) by multiple strains of Bymoviruses and could therefore play a using agrochemicals to control virus vectors is seldom efficient central role in durable virus resistance breeding in barley. The from economic or ecological perspectives. Therefore, crop pro- geographic distribution of functional alleles of rym11 in East tection based on naturally occurring virus resistance is key to Asia suggests adaptive selection for resistance in this region. minimizing losses and achieving sustainable crop yields. Orthologues of HvPDIL5-1 or related members of the PDI gene Positive-strand RNA viruses represent the largest group of family potentially provide susceptibility factors to viruses across plant viruses (3). They cause a very high proportion of the im- portant infectious virus diseases in agriculture (4, 5). Such plant animal and plant kingdoms. viruses carry a reduced genome that encodes a limited set of – — Author contributions: F.O. and N.S. designed research; T.L. mapped and identified the can- functional proteins (4 10 viral proteins) insufficient to com- didate gene HvPDIL5-1; P.Y., A. Habekuss, G.H., A. Himmelbach, and J.K. performed research; plete the entire virus replication and proliferation cycle (6). In- P.Y., T.L., B.S., B.K., R.A., and U.S. analyzed data; and P.Y. and N.S. wrote the paper. stead, over evolutionary time, viruses recruited host factors to Conflict of interest statement: A patent application has been filed relating to this work. perform the infectious life cycle (7). This dependence on host factors establishes a possibility that plants can evolve escape, tol- This article is a PNAS Direct Submission. erance, or resistance mechanisms to ameliorate the consequences Freely available online through the PNAS open access option. of viral infection. The absence of essential host factors could in- Data deposition: The sequences reported in this paper have been deposited in the EMBL terfere with the infection process or restrict proliferation (8) lead- database (accession nos. PRJEB4765 and HG793095). ing to either mono- or polygenic recessive resistance (5). Prominent 1Present address: The Sainsbury Laboratory, Norwich Research Park, Norwich, NR4 7UH, examples of such susceptibility factors that are conserved in mul- United Kingdom. tiple plant–virus systems are the EUKARYOTIC TRANSLATION 2F.O. and N.S. contributed equally to this work. INITIATION FACTORS (EIF)4E, iso4E, 4G, and iso4G (9). 3To whom correspondence should be addressed. E-mail: [email protected]. Translation initiation factors may interact directly with viral RNA This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10. where they catalyze the initiation of translation of viral polyproteins 1073/pnas.1320362111/-/DCSupplemental. 2104–2109 | PNAS | February 11, 2014 | vol. 111 | no. 6 www.pnas.org/cgi/doi/10.1073/pnas.1320362111 Downloaded by guest on September 24, 2021 was therefore a likely candidate for rym11-based resistance. The allele carrying the 1,375-bp deletion was named rym11-a. Functional Validation of HvPDIL5-1 as a Susceptibility Factor for Bymovirus Infection. We used three independent approaches to validate the hypothesis that HvPDIL5-1 is a susceptibility factor for bymovirus infection. First, we screened an EMS-induced mutant population of barley by targeting induced local lesions in genomes (TILLING) (21). Two independent mutants 9699 and 10253 were identified each carrying a premature STOP codon in the coding sequence (CDS) of HvPDIL5-1 (SI Appendix, Table S1 and Fig. 1B). M3 progeny of the originally heterozygous M2 plants segregated for virus resistance. After phenotyping, the plants were genotyped for the presence of the mutation. All homozygous mutant M3 plants were found to be completely re- sistant. Homozygous wild-type and heterozygous M3 plants were predominantly susceptible with infection rates comparable to the susceptible controls (Table 1 and SI Appendix, Table S2). Re- sistance tests were replicated twice in M4 progeny of a homozy- gous mutant and a wild-type M3 plant of each of the mutant lines 9699 and 10253, respectively. All homozygous mutant M4 plants were tested resistant. Homozygous wild-type M4 progeny were susceptible, with infection rates between 66% and 100%, similar to susceptible controls (Table 1 and SI Appendix, Table S2 and Fig. S3). Mechanically infected homozygous wild-type HvPDIL5- 1 M4 progenies showed the characteristic yellow discoloration during vegetative growth stage (Fig. 1C), stunted growth at heading stage (Fig. 1D), as well as late maturation (Fig. 1E). Mock in- oculated homozygous mutant M4 individuals did not show any detectable difference in overall growth habit at heading and Fig. 1. Map-based