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Fine Mapping and Candidate Gene Discovery of the Soybean Mosaic Virus Resistance Gene , Rsv 4

Soybean mosaic virus (SMV) is a prevalent virus infecting soybean (Glycine max L. Merr) worldwide. The incorporation of Rsv4, conferring resistance to all currently known strains in the United States, can assist in creating durable virus resistance in soybean. Additionally, lines heterozygous at the Rsv4 locus often express a late susceptible phenotype, showing symptoms only in mid to late vegetative growth. In this study the wholegenome shotgun sequence (WGS) of soybean was utilized for fi ne mapping and examining potential Rsv4 gene candidates in two populations. Six markers, designed from the WGS, were used to localize Rsv4 in the same, 1.3-cM region in both mapping populations, a physical interval of less than 100 kb on chromosome 2. This region contained no sequences previously related to virus resistance, namely nucleotide binding site-leucine rich repeat gene sequences or eukaryotic translation initiation factors. Instead, sequence analysis revealed several predicted transcription factors and unknown protein products. We conclude that Rsv4 likely belongs to a new class of resistance genes that interfere with viral infection and cell-to-cell movement, and delay vascular movement. SOYBEAN MOSAIC VIRUS (SMV) (genus Potyvirus, family Potyviridae) is one of the most prevalent viruses infecting soybean, causing losses in yield and quality annually. SMV also acts synergistically with Bean pod mottle (BPMV) (genus Comovirus, family Comoviridae) to further reduce yields up to 85% (Ross, 1968). As the geographical range of Cerotoma trifurcata, a beetle vector of BPMV, increases (Giesler et al., 2002), and the populations of the soybean aphid (Aphis glycines), a vector of SMV (Wang et al., 2006) increase, loss in soybean yield caused by viruses is expected to increase (Burrows et al., 2005). It is critical to have durable resistance to both viruses in soybean; however, resistance to BPMV has not yet been identifi ed genetically. For SMV, three resistance genes, Rsv1, Rsv3, and Rsv4, have been genetically identifi ed and deployed in United States germplasm for disease control. However, emergence of resistance-breaking strains of SMV has been documented in other regions of the world (Choi et al., 2005; Koo et al., 2005). Two genes for resistance to SMV, Rsv1 and Rsv3, are strain-specifi c and have been associated with a typical hypersensitive response (HR), resulting in local or systemic necrosis to certain strains of the seven U.S. strain groups (Saghai Maroof et al., 2008). Nine Rsv1 resistance Published in The Plant Genome 3:14–22. Published 7 May 2010. doi: 10.3835/plantgenome2009.07.0020 © Crop Science Society of America 5585 Guilford Rd., Madison, WI 53711 USA An open-access publication All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher. M.A. Saghai Maroof, D.M. Tucker, J.A. Skoneczka, and B.C. Bowman, Dep. of Crop & Soil Environmental Sciences, Virginia Tech, Blacksburg, VA, 20461. S. Tripathy, Virginia Bioinformatics Inst., Virginia Tech, Blacksburg, VA, 24061. S.A. Tolin, Dep. of Plant Pathology, Physiology & Weed Science, Virginia Tech, Blacksburg, VA 24061. Received 20 July 2009. *Corresponding author