Identification and molecular characterization of Vf -like candidate genes in cultivated apples and selections from Malus sieversii .

摘要

The genetic locus for resistance to apple scab most frequently used in apple breeding is Vf, derived from Malus floribunda 821. For the Vf locus a cluster of four resistance gene paralogs encoding receptor-like proteins (RLP) with similarity to the tomato Cf resistance genes is known. Based on nucleotide alignments of published sequences of HcrVf1, HcrVf2, and HcrVf3, PCR primers were designed from the variable leucine-rich repeat (LRR) C1 subdomain. PCR products with high amino acid identity (85 to 100%) to HcrVf1 and HcrVf2 were obtained not only from M. floribunda 821 and Vf cultivars, but also from other apple scab resistance sources, such as 'Russian Seedling' R12740-7A or some 'Antonovka' accessions tested. A series of thirteen HcrVf candidate genes have been partly cloned from the PCR fragments spanning N-terminal LRRs 20-30. Expression analyses and mapping were focused on two specific Vf-homologous candidate genes, Vf1RSA and Vf2ARD, identified in resistant Malus genotypes known for carrying other scab resistance genes than Vf. RT-PCR experiments showed that Vf1RSA as well as the Vf2ARD are expressed under pathogen-free conditions. The results of a quantitative PCR-based transcription profiling performed for Vf2ARD suggest that this gene is scab-inducible in some resistant cultivars. Vf1RSA has been mapped, so far, without any recombination to the known Vf gene cluster on linkage group LG 1. The second candidate gene Vf2ARD is separated from the Vf gene cluster with a genetic distance of about 2 cM and might be a member of a second Vf-like locus on apple linkage group LG 1.