Genetic and Genomic Analysis of Brachypodium distachyon Resistance to Barley Stripe Mosaic Virus Infection

Barley stripe mosaic virus (BSMV) can elicit a wide ranging variety of phenotypic responses in its native host is barley (Hordeum vulgare L.,) and other field and experimental hosts. BSMV resistance in barley has been the subject of several studies, and the virus also elicits a differential infection response in several Brachypodium distachyon lines. Among accessions tested, the Bd3-1 inbred line exhibits resistance to the ND18 strain of BSMV and produces no visible symptoms or virus, whereas Bd21 is susceptible and infection results in an intense mosaic phenotype accompanied by large amounts of virus. We have used recombinant inbred lines (RIL) generated from Bd21 X Bd3-1 crosses and genomics resources available for Brachypodium to map the resistance gene, which we have provisionally designated BSR1. Inoculation of ND18 to an F2 population from a Bd21 X Bd3-1 cross showed that resistance is encoded by a single dominant gene, in contrast to barley resistance genes, which are recessive. A genetic linkage map of an F6 RIL population was constructed by using SNP markers derived from the Bd21 sequence to map the BSR1 locus to within 705 KB of the distal end the short arm of chromosome 3. A more refined map constructed with CAPS and InDel markers narrowed BSR1 to a 23 KB (~1.2 cM) interval between two CAPS markers. Additional analysis of the BSR1 interval in a Bd3-1 BAC library revealed a NBS-LRR domain protein was proposed as the candidate of BSR1 gene whose nature will be discussed.