title: Dissection of Two Complex Clusters of Resistance Genes in Lettuce (Lactuca sativa).
abstract: Of the over 50 phenotypic resistance genes mapped in lettuce, 25 colocalize to three major resistance clusters (MRC) on chromosomes 1, 2, and 4. Similarly, the majority of candidate resistance genes encoding nucleotide binding-leucine rich repeat (NLR) proteins genetically colocalize with phenotypic resistance loci. MRC1 and MRC4 span over 66 and 63 Mb containing 84 and 21 NLR-encoding genes, respectively, as well as 765 and 627 genes that are not related to NLR genes. Forward and reverse genetic approaches were applied to dissect MRC1 and MRC4. Transgenic lines exhibiting silencing were selected using silencing of β-glucuronidase as a reporter. Silencing of two of five NLR-encoding gene families resulted in abrogation of nine of 14 tested resistance phenotypes mapping to these two regions. At MRC1, members of the coiled coil-NLR-encoding RGC1 gene family were implicated in host and nonhost resistance through requirement for Dm5/8- and Dm45-mediated resistance to downy mildew caused by Bremia lactucae as well as the hypersensitive response to effectors AvrB, AvrRpm1, and AvrRpt2 of the nonpathogen Pseudomonas syringae. At MRC4, RGC12 family members, which encode toll interleukin receptor-NLR proteins, were implicated in Dm4-, Dm7-, Dm11-, and Dm44-mediated resistance to B. lactucae. Lesions were identified in the sequence of a candidate gene within dm7 loss-of-resistance mutant lines, confirming that RGC12G confers Dm7.
authors: Genome Center and Department of Plant Sciences, University of California-Davis, CA 95616, U.S.A.
authors: Marilena
authors: M
authors: Christopoulou
authors: Genome Center and Department of Plant Sciences, University of California-Davis, CA 95616, U.S.A.
authors: Leah K
authors: LK
authors: McHale
authors: Genome Center and Department of Plant Sciences, University of California-Davis, CA 95616, U.S.A.
authors: Alex
authors: A
authors: Kozik
authors: Genome Center and Department of Plant Sciences, University of California-Davis, CA 95616, U.S.A.
authors: Sebastian
authors: S
authors: Reyes-Chin Wo
authors: Genome Center and Department of Plant Sciences, University of California-Davis, CA 95616, U.S.A.
authors: Tadeusz
authors: T
authors: Wroblewski
authors: Genome Center and Department of Plant Sciences, University of California-Davis, CA 95616, U.S.A.
authors: Richard W
authors: RW
authors: Michelmore
mesh_terms: D032461:Chromosomes, Plant; D060467:Disease Resistance / Q000235:genetics*; D018545:Lactuca / Q000235:genetics* / Q000382:microbiology; D005810:Multigene Family; D009154:Mutation; D009868:Oomycetes / Q000472:pathogenicity; D010935:Plant Diseases / Q000235:genetics* / Q000382:microbiology; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D030821:Plants, Genetically Modified; D044224:Pseudomonas syringae / Q000472:pathogenicity; D020449:Repetitive Sequences, Amino Acid
chemical_list: D010940:Plant Proteins