Prediction of the optimum hybridization conditions of dot-blot-SNP analysis using estimated melting temperature of oligonucleotide probes

Novel glucosinolate composition lacking 4-methylthio-3-butenyl glucosinolate in Japanese white radish (Raphanus sativus L.)

Genetic analysis and gene mapping of the 4-methylthio-3-butenyl glucosinolate-less trait of white radish were performed and a white radish cultivar with new glucosinolate composition was developed. A spontaneous mutant having significantly low 4-methylthio-3-butenyl glucosinolate (4MTB-GSL) content was identified from a landrace of Japanese white radish (Raphanus sativus L.) through intensive evaluation of glucosinolate profiles of 632 lines including genetic resources and commercial cultivars using high-performance liquid chromatography (HPLC) analysis. A line lacking 4MTB-GSL was developed using the selected mutant as a gene source. Genetic analyses of F1, F2, and BC1F1 populations of this line suggested that the 4MTB-GSL-less trait is controlled by a single recessive allele. Using SNP and SCAR markers, 96 F2 plants were genotyped, and a linkage map having nine linkage groups with a total map distance of 808.3 cM was constructed. A gene responsible for the 4MTB-GSL-less trait was mapped between CL1753 and CL5895 at the end of linkage group 1. The genetic distance between these markers was 4.2 cM. By selfing and selection of plants lacking 4MTB-GSL, a new cultivar, 'Daikon parental line No. 5', was successfully developed. This cultivar was characterized by glucoerucin, which accounted for more than 90% of the total glucosinolates (GSLs). The total GSL content in roots was ca. 12 μmol/g DW, significantly lower than those in common white radish cultivars. Significance of this line in radish breeding is discussed.

QTL analysis using SNP markers developed by next-generation sequencing for identification of candidate genes controlling 4-methylthio-3-butenyl glucosinolate contents in roots of radish, Raphanus sativus L

SNP markers for QTL analysis of 4-MTB-GSL contents in radish roots were developed by determining nucleotide sequences of bulked PCR products using a next-generation sequencer. DNA fragments were amplified from two radish lines by multiplex PCR with six primer pairs, and those amplified by 2,880 primer pairs were mixed and sequenced. By assembling sequence data, 1,953 SNPs in 750 DNA fragments, 437 of which have been previously mapped in a linkage map, were identified. A linkage map of nine linkage groups was constructed with 188 markers, and five QTLs were detected in two F(2) populations, three of them accounting for more than 50% of the total phenotypic variance being repeatedly detected. In the identified QTL regions, nine SNP markers were newly produced. By synteny analysis of the QTLs regions with Arabidopsis thaliana and Brassica rapa genome sequences, three candidate genes were selected, i.e., RsMAM3 for production of aliphatic glucosinolates linked to GSL-QTL-4, RsIPMDH1 for leucine biosynthesis showing strong co-expression with glucosinolate biosynthesis genes linked to GSL-QTL-2, and RsBCAT4 for branched-chain amino acid aminotransferase linked to GSL-QTL-1. Nucleotide sequences and expression of these genes suggested their possible function in 4MTB-GSL biosynthesis in radish roots.

Extensive chromosome homoeology among Brassiceae species were revealed by comparative genetic mapping with high-density EST-based SNP markers in radish (Raphanus sativus L.)

A linkage map of expressed sequence tag (EST)-based markers in radish (Raphanus sativus L.) was constructed using a low-cost and high-efficiency single-nucleotide polymorphism (SNP) genotyping method named multiplex polymerase chain reaction–mixed probe dot-blot analysis developed in this study. Seven hundred and forty-six SNP markers derived from EST sequences of R. sativus were assigned to nine linkage groups with a total length of 806.7 cM. By BLASTN, 726 markers were found to have homologous genes in Arabidopsis thaliana, and 72 syntenic regions, which have great potential for utilizing genomic information of the model species A. thaliana in basic and applied genetics of R. sativus, were identified. By construction and analysis of the genome structures of R. sativus based on the 24 genomic blocks within the Brassicaceae ancestral karyotype, 23 of the 24 genomic blocks were detected in the genome of R. sativus, and half of them were found to be triplicated. Comparison of the genome structure of R. sativus with those of the A, B, and C genomes of Brassica species and that of Sinapis alba L. revealed extensive chromosome homoeology among Brassiceae species, which would facilitate transfer of the genomic information from one Brassiceae species to another.