Genetic diversity and genomic distribution of homologs encoding NBS-LRR disease resistance proteins in sunflower.
Three-fourths of the recognition-dependent disease resistance genes (R-genes) identified in plants encode nucleotide binding site (NBS) leucine-rich repeat (LRR) proteins. NBS-LRR homologs have only been isolated on a limited scale from sunflower (Helianthus annuus L.), and most of the previously identified homologs are members of two large NBS-LRR clusters harboring downy mildew R-genes. We mined the sunflower EST database and used comparative genomics approaches to develop a deeper understanding of the diversity and distribution of NBS-LRR homologs in the sunflower genome. Collectively, 630 NBS-LRR homologs were identified, 88 by mining a database of 284,241 sunflower ESTs and 542 by sequencing 1,248 genomic DNA amplicons isolated from common and wild sunflower species. DNA markers were developed from 196 unique NBS-LRR sequences and facilitated genetic mapping of 167 NBS-LRR loci. The latter were distributed throughout the sunflower genome in 44 clusters or singletons. Wild species ESTs were a particularly rich source of novel NBS-LRR homologs, many of which were tightly linked to previously mapped downy mildew, rust, and broomrape R-genes. The DNA sequence and mapping resources described here should facilitate the discovery and isolation of recognition-dependent R-genes guarding sunflower from a broad spectrum of economically important diseases. Sunflower nucleotide and amino acid sequences have been deposited in DDBJ/EMBL/GenBank under accession numbers EF 560168-EF 559378 and ABQ 58077-ABQ 57529.
Radwan
Osman
O
Center for Applied Genetic Technologies, The University of Georgia, 111 Riverbend Road, Athens, GA 30602, USA.
Gandhi
Sonali
S
Heesacker
Adam
A
Whitaker
Brett
B
Taylor
Chris
C
Plocik
Alex
A
Kesseli
Richard
R
Kozik
Alexander
A
Michelmore
Richard W
RW
Knapp
Steven J
SJ
D000595:Amino Acid Sequence; D001483:Base Sequence; D002874:Chromosome Mapping; D017124:Conserved Sequence; D018744:DNA, Plant / Q000235:genetics; D030561:Databases, Nucleic Acid; D020224:Expressed Sequence Tags; D005658:Fungi / Q000472:pathogenicity; D014644:Genetic Variation; D018745:Genome, Plant; D006368:Helianthus / Q000235:genetics* / Q000382:microbiology; D008969:Molecular Sequence Data; D009868:Oomycetes / Q000472:pathogenicity; D010802:Phylogeny; D010935:Plant Diseases / Q000235:genetics / Q000382:microbiology; D010940:Plant Proteins / Q000235:genetics
D018744:DNA, Plant; D010940:Plant Proteins