The anthracnose resistance locus Co-4 of common bean is located on chromosome 3 and contains putative disease resistance-related genes.
The broadest based resistance to anthracnose of common bean ( Phaseolus vulgaris L.) is conferred by the Co-4 locus. We sequenced a bacterial artificial chromosome clone harboring part of the Co-4 locus of the bean genotype Sprite and assembled a single contig of 106.5 kb for functional annotation. This region contained five copies of the COK-4 gene that encodes for a serine threonine kinase protein previously mapped to the Co-4 locus and 19 novel genes with no similarity to any previously identified genes of common bean. Several putative genes of the Co-4 locus seemed to be expressed as they matched perfectly with bean expressed sequence tags. The expression of the COK-4 genes was assessed by reverse transcription (RT)-PCR, and a single 850-bp cDNA fragment was sequenced and compared with the genomic sequences of the COK-4 homologs. Although the COK-4 cDNA was isolated from a different bean cultivar, it showed high similarity (95%) to the exons of genes BA17 and BA21, suggesting that they were expressed. In a phylogenetic tree including all currently available Pto-like sequences from Phaseolus species, the COK-4 homologs formed a single cluster with the Pto gene, whereas two sequences from P. coccineus and all sequences of P. vulgaris formed two closely related clusters. The Co-4 locus was physically mapped to the short arm of bean chromosome 3, which corresponds to linkage group B8. This study represents a first step in gaining an understanding of the genomic organization of an anthracnose resistance locus of common bean and provides molecular data for comparative analysis with other plant species.
Melotto
M
M
Departamento de Fitopatologia, Laboratório de Genética Molecular, ESALQ, Universidade de São Paulo, C.P. 9, 13418-900, Piracicaba, SP, Brazil. melottom@msu.edu
Coelho
M F
MF
Pedrosa-Harand
A
A
Kelly
J D
JD
Camargo
L E A
LE
D001203:Ascomycota; D001483:Base Sequence; D002874:Chromosome Mapping; D022202:Chromosomes, Artificial, Bacterial; D018076:DNA, Complementary / Q000235:genetics; D016521:Electrophoresis, Gel, Pulsed-Field; D017343:Genes, Plant / Q000235:genetics; D007113:Immunity, Innate / Q000235:genetics*; D008969:Molecular Sequence Data; D027805:Phaseolus / Q000235:genetics* / Q000382:microbiology; D010802:Phylogeny; D010935:Plant Diseases / Q000382:microbiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017422:Sequence Analysis, DNA
D018076:DNA, Complementary