Theor Appl Genet (2012) 124:1005–1015 DOI 10.1007/s00122-011-1764-8 123 ORIGINAL PAPER Two loci in sorghum with NB-LRR encoding genes confer resistance to Colletotrichum sublineolum Moses Biruma · Tom Martin · Ingela Fridborg · Patrick Okori · Christina Dixelius Received: 21 September 2011 / Accepted: 23 November 2011 / Published online: 6 December 2011  Springer-Verlag 2011 Abstract The aim of this work was to identify plant resis- tance genes to the sorghum anthracnose fungus Colletotri- chum sublineolum. cDNA-AFLP transcript proWling on two contrasting sorghum genotypes inoculated with C. subli- neolum generated about 3,000 informative fragments. In a Wnal set of 126 sequenced genes, 15 were identiWed as biotic stress related. Seven of the plant-derived genes were selected for functional analysis using a Brome mosaic virus-based virus-induced gene silencing (VIGS) system followed by fungal inoculation and quantitative real-time PCR analysis. The candidate set comprised genes encoding resistance proteins (Cs1A, Cs2A), a lipid transfer protein (SbLTP1), a zinc Wnger-like transcription factor (SbZnTF1), a rice defensin-like homolog (SbDEFL1), a cell death related protein (SbCDL1), and an unknown gene harboring a casein kinase 2-like domain (SbCK2). Our results demonstrate that down-regulation of Cs1A, Cs2A, SbLTP1, SbZnF1 and SbCD1 via VIGS, signiWcantly compromised the resistance response while milder eVects were observed with SbDEFL1 and SbCK2. Expanded genome analysis revealed that Cs1A and Cs2A genes are located in two diVerent loci on chromosome 9 closely linked with dupli- cated genes Cs1B and Cs2B, respectively. The nucleotide binding-leucine rich repeat (NB-LRR) encoding Cs gene sequence information is presently employed in regional breeding programs. Introduction In all natural environments, plants are rarely able to grow without attempted pathogen colonization and have evolved both passive and active mechanisms to prevent infection. Active defense mechanisms are based upon an early recog- nition of the intruder followed by appropriate responses. Like animals, plants have evolved two distinct categories of immune receptors, each of which recognizes non-self molecules (reviewed in Chisholm et al. 2006; Cui et al. 2009). The Wrst class, which contributes to basal defense, involves membrane-resident pattern recognition receptors that detect conserved microbe-associated molecular pat- terns (MAMPs) such as bacterial Xagellin or fungal chitin. This Wrst line of defense against pathogens is reminiscent of innate immunity in vertebrates. The expression of basal resistance to invasive pathogens is a crucial protective defense barrier. Without it, plants become susceptible to even mild infections and are less likely to survive in a competitive environment. The second strategy is eVector-trig- gered immunity (ETI) represented by resistance (R) proteins, which are mainly intracellular, having the capacity to directly or indirectly detect isolate-speciWc pathogen eVector proteins, encoded by avirulence (Avr) genes. Variants of Communicated by A. Paterson. Electronic supplementary material The online version of this article (doi:10.1007/s00122-011-1764-8) contains supplementary material, which is available to authorized users. M. Biruma · P. Okori Department of Crop Science, Makerere University, P.O. Box 7062, Kampala, Uganda M. Biruma National Agriculture Research Organisation, P.O. Box 295, Entebbe, Uganda T. Martin · I. Fridborg · C. Dixelius (&) Department of Plant Biology and Forest Genetics, Uppsala Biocenter, SLU, P.O. Box 7080, 750 07 Uppsala, Sweden e-mail: Christina.Dixelius@slu.se