Mapping and candidate gene screening of tomato Cladosporium fulvum-resistant gene Cf-19, based on high-throughput sequencing technology.

BACKGROUND: Tomato leaf mold is a common disease in tomato cultivation. This disease is caused by Cladosporium fulvum, which has many physiological races and differentiates rapidly. Cf genes confer resistance to C. fulvum, and the C. fulvum-tomato pathosystem is a model for the study of gene-for-gene interactions. Plants carrying the Cf-19 gene show effective resistance to C. fulvum in the field, and can be used in breeding and resistance mechanism studies as new resistant materials. In this study, we used F2 bulk specific-locus amplified fragment sequencing (SLAF-seq) and parental resequencing methods to locate and characterize the Cf-19 gene.

RESULTS: A total of 4108 Diff_markers and three association regions were found in association analysis. A 2.14-Mb region containing seven Cf-type genes was identified in further analysis based on data from SLAF-seq and parental resequencing. Two candidate genes, Solyc01g006550.2.1 and Solyc01g005870.1.1, were screened out by quantitative real-time PCR (qRT-PCR) analysis. Sequence analysis showed that Solyc01g006550.2.1 (an allelic locus of Cf-0) in CGN18423 was a novel homologue of the Cladosporium resistance gene Cf-9 (Hcr9s) in the Cf-4/9 locus. The marker P7, which cosegregated with the resistant trait, was developed based on sequence mutation of the Solyc01g006550.2.1 locus in CGN18423.

CONCLUSIONS: The Cf-19 gene was mapped to the short arm of chromosome 1. The candidate genes Solyc01g006550.2.1 and Solyc01g005870.1.1 showed related amino acid sequence structures and expression patterns. Solyc01g006550.2.1 had a close evolutionary relationship with the functional Hcr9 members Cf-4 and Cf-9, and was very different from non-functional members. The results from this study will facilitate the breeding of cultivars carrying the Cf-19 gene and provide a basis for further gene cloning, resistance gene evolution and plant resistance mechanism studies.