BackgroundWater-soluble anthocyanin pigments are important ingredients in health-improving supplements and valuable for the food industry. Although great attention has been paid to the breeding and production of crops containing high levels of anthocyanin, genetic variation in red or purple cabbages (Brassica oleracea var. capitata F. rubra) has not yet been characterized at the molecular level. In this study, we identified the mechanism responsible for the establishment of purple color in cabbages.ResultsBoMYBL2–1 is one of the regulatory genes in the anthocyanin biosynthesis pathway in cabbages. It is a repressor whose expression is inversely correlated to anthocyanin synthesis and is not detectable in purple cabbages. Sequence analysis of purple cabbages revealed that most lacked BoMYBL2–1 coding sequences, although a few had a substitution in the region of the promoter 347 bp upstream of the gene that was associated with an absence of BoMYBL2–1 expression. Lack of transcriptional activity of the substitution-containing promoter was confirmed using transgenic Arabidopsis plants transformed with promoter::GUS fusion constructs. The finding that the defect in BoMYBL2–1 expression was solely responsible for purple coloration in cabbages was further demonstrated using genomic PCR and RT-PCR analyses of many other structural and regulatory genes in anthocyanin biosynthesis. Molecular markers for purple cabbages were developed and validated using 69 cabbage lines.ConclusionExpression of BoMYBL2–1 was inversely correlated to anthocyanin content, and purple color in cabbages resulted from a loss of BoMYBL2–1 expression, caused by either the promoter substitution or deletion of the gene. This is the first report of molecular markers that distinguish purple cabbages. Such markers will be useful for the production of intraspecific and interspecific hybrids for functional foods, and for industrial purposes requiring high anthocyanin content.Electronic supplementary materialThe online version of this article (10.1186/s12870-018-1290-9) contains supplementary material, which is available to authorized users.

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Heat-shock proteins (HSPs) and heat-shock transcription factors (HSFs) are central components of the heat-shock regulatory network and are involved in cellular responses to various forms of stresses. To examine the differences in heat shock responses (HSRs) of two comparable inbred lines of Chinese cabbage (Brassica rapa), 51 genes were selected from 130,000 Brassica rapa ESTs that belong to an HSF and six HSP families and examined their expression using RT-PCR. Two Chinese cabbage inbred lines, Chiifu and Kenshin, have different geographic origins, in that Chiifu is from temperate regions, while Kenshin is from subtropical and tropical regions. Among the 51 genes, six genes were induced, eleven were stimulated, and three were reduced in both inbred lines in response to heat shock (HS) treatment. However, eleven genes were differentially expressed between the two inbred lines. Among these genes, several appear to be involved in normal growth and chloroplast development. These data suggest that the two Chinese cabbage inbred lines have similar HSRs, but the unique HSRs allow Kenshin to develop at higher temperatures.

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Global warming accelerates the development of high temperature (HT)- and high humidity (HH)-tolerant varieties. This is further facilitated by the identification of HTHH-tolerant genes and the development of molecular markers based on these genes. To identify genes involved in HTHH tolerance in cabbage (Brassica oleracea var. capitata), we performed RNA-seq analysis of two inbred lines, BN1 (HTHH-tolerant) and BN2 (HTHH-susceptible), and selected trehalose 6- phosphate phosphatase I-2 (BoTPPI-2) as one of the HTHH-tolerant-associated genes. We also developed a segregating F2 population from a cross between BN1 and BN2. RNA-seq results showed that BoTPPI-2 transcript levels were high in the HTHH-tolerant inbred line BN1, but not detectable in the HTHH-susceptible inbred line BN2. The expression pattern of BoTPPI-2 was not related to the expression of heat shock-related genes. Soft rot resistance, used as an indicator of HTHH tolerance, was higher in BN1 than in BN2. F2 individuals similar to BN1 with respect to phenotype appeared to be HTHH-tolerant, whereas BN2-types were susceptible to HTHH. Analysis of the genomic DNA revealed the presence of a long terminal repeat (LTR; ca. 4.6 kb) in the ninth intron of the BoTPPI-2_BN2 allele, thereby suppressing its transcription and exhibiting HTHH phenotype. Except for the LTR insertion, the sequence of BoTPPI-2_BN2 was almost identical to that of BoTPPI-2_BN1. On the basis of the LTR and BoTPPI-2 sequences, we developed a molecular marker to identify HTHH-tolerant genotypes and validated its efficiency using F2 individuals, inbred lines, and cultivars from diverse sources. The marker explained the genetic basis of HTHH tolerance in at least 80%, but not 100%, of the cabbage genotypes. Thus, additional markers associated with HTHH tolerance are needed for perfect selection.