Submitted to: Plant and Animal Genome Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 10/15/2002
Publication Date: 1/15/2003
Citation: Gao, M., Li, G.B., Yang, B., Farnham, M.W., Quiros, C. Search for candidate genes for downy mildew resistance in broccoli. Plant and Animal Genome XI Conference Proceedings. 2003. Abstract No. 476.
Technical Abstract: We found on Arabidopsis chromosome V the homolog for a PCR-based marker (OPM16-750) linked to cotyledon-stage downy mildew resistance in broccoli. It was located 0.53 Mb downstream from IPM2-9 (isopropyl malate synthase-like, side chain elongation of aliphatic glucosinolates; Brassica homolog is BoGSL-Elong). Co-segregation analysis of a broccoli F2 population segregating for downy mildew resistance and IPM2-9 demonstrated that indeed the BoGSL-Elong gene was linked to cotyledon-stage downy mildew resistance. A putative disease resistance LRR-gene (At5g23400) was found between marker OPM16 and IMP2-9 at 0.18 Mb and 0.35 Mb, respectively. Screening a broccoli BAC library with primers from At5g23400 disclosed two positive BAC clones. After sequencing the two broccoli homologs we found that they share 91% identity between them. Co-segregation of two copies with BoGSL-Elong in a broccoli by cauliflower F2 population segregating for glucosinolates disclosed that only one of these two homologs (named Dmc1) was linked to BoGSL-Elong. Therefore the other homolog was eliminated as a possible candidate gene for downy mildew resistance. Dmc1 has 1770 bases, is intronless and has 86% identity with At5g23400. Another putative disease resistance LRR-gene (At5g22690) was found in Arabidopsis upstream IMP2-9 (0.16 Mb apart). We have identified three broccoli BACs with homologs to this gene and are in the process of sequencing them. Co-segregation analysis of these genes and downy mildew resistance will be used to determine the most likely candidate gene among these homologs. This will be confirmed by functionality analysis and complementary transformation.