The Chinese cabbage is a crop belonging to the family Cruciferae; very few studies have focused on the analysis of gene expression in this economically important crop. In this study, we used real-time quantitative polymerase chain reaction to identify the control genes that are the most stably expressed in a given set of tissues and under conditions of drought stress and downy mildew infection. We characterized the transcript stability of nine candidate reference genes, namely, those encoding glyceraldehyde-3-phosphate dehydrogenase (GAPDH), ubiquitin (Ubc), elongation-factor-1-α (EF-1-α), adenine phosphoribosyltransferase (Apr), clathrin, cyclophilin (Cyp), tubulin (Tub), Actin, and 18s rRNA, using the geNorm and Normfinder software programs. The results of a geNorm analysis indicated that EF-1-α and Apr were the most suitable reference genes among the given set of tissues and that GAPDH and Ubc were the most stable genes under conditions of drought stress and downy mildew infection. Furthermore, the results of an analysis performed using the Normfinder software program indicated EF-1-α to be the best normalization factor in the given set of tissues and under conditions of downy mildew infection and GAPDH to be the best factor under drought stress conditions. The results of the geNorm analysis also helped determine the minimum number of genes required to calculate a reliable normalization factor. A study on the variability of expression of PSY expression showed that the relative quantification of this gene varied depending on the internal control and the number of internal controls used, thus highlighting the importance of the choice of internal controls in such experiments.

Chinese cabbage is the most consumed leafy crop in East Asian countries. However, premature bolting induced by continuous low temperatures severely decreases the yield and quality of the Chinese cabbage, and therefore restricts its planting season and geographic distribution. In the past 40 years, spring Chinese cabbage with strong winterness has been selected to meet the market demand. Here, we report a genome variation map of Chinese cabbage generated from the resequencing data of 194 geographically diverse accessions of three ecotypes. In-depth analyses of the selection sweeps and genome-wide patterns revealed that spring Chinese cabbage was selected from a specific population of autumn Chinese cabbage around the area of Shandong peninsula in northern China. We identified 23 genomic loci that underwent intensive selection, and further demonstrated by gene expression and haplotype analyses that the incorporation of elite alleles of VERNALISATION INSENTIVE 3.1 (BrVIN3.1) and FLOWER LOCUS C 1 (BrFLC1) is a determinant genetic source of variation during selection. Moreover, we showed that the quantitative response of BrVIN3.1 to cold due to the sequence variations in the cis elements of the BrVIN3.1 promoter significantly contributes to bolting-time variation in Chinese cabbage. Collectively, our study provides valuable insights into the genetic basis of spring Chinese cabbage selection and will facilitate the breeding of bolting-resistant varieties by molecular-marker-assisted selection, transgenic or gene editing approaches.

Chinese cabbage varieties with orange inner leaves are of interest due to their attractive appearance and high carotenoid content. Previously, a recessive locus, Br-or, that confers this trait was mapped to linkage group A09 in Brassica rapa, and Bra031539 was identified as the candidate gene. We used a backcross population consisting of 1,392 individuals for fine mapping; three linked markers delimited the Br-or locus to a region of 9.47 kb, which contained only one predicted functional gene, Bra031539 (the carotenoid isomerase gene BrCRTISO). We identified two bacterial artificial chromosome (BAC) clones carrying Br-or and confirmed that this allele of BrCRTISO confers the mutant phenotype by sequencing. Many DNA sequence variations are present in Br-or, including a 90-bp DNA deletion in the promoter and a 501-bp insertion at the 3′ end of the gene. GUS staining showed that the spatial expression of BrCRTISO was perfectly coincident with the site of carotenoid synthesis and that the 90-bp deletion in the promoter slightly downregulated expression of the gene. Using an in vitro enzyme assay, we showed that the mutant Br-or protein cannot convert prolycopene to all-trans-lycopene. Light has a positive effect on the expression of carotenoid biosynthesis genes, except for beta-ring carotene hydroxylase (CHXB), and this coincided with the increase in total lycopene and β-carotene in the Br-or mutant. We also demonstrated that loss of BrCRTISO function, upregulation of the upstream genes, and downregulation of downstream genes lead to the accumulation of prolycopene and confer an orange color to the inner head leaves in Chinese cabbage. Keywords Brassica rapa L. ssp. pekinensis . Orange leaf . Br-or . BrCRTISO . Carotenoid biosynthesis Abbreviations CHXB Beta-ring carotene hydroxylase DH Doubled haploid GAPDH Glyceraldehyde-3-phosphate dehydrogenase IPI Isopentenyl pyrophosphate isomerase LCYB Lycopene beta-cyclase LCYE Lycopene epsilon-cyclase PDS Phytoene desaturase PSY Phytoene synthase VDE Violaxanthin de-epoxidase ZDS Zeta-carotene desaturase ZEP Zeaxanthin epoxidase

SummaryRecombination is a major mechanism generating genetic diversity, but the control of the crossover rate remains a key question. In Brassica napus (AACC, 2n = 38), we can increase the homologous recombination between A genomes in AAC hybrids. Hypotheses for this effect include the number of C univalent chromosomes, the ratio between univalents and bivalents and, finally, which of the chromosomes are univalents.To test these hypotheses, we produced AA hybrids with zero, one, three, six or nine additional C chromosomes and four different hybrids carrying 2n = 32 and 2n = 35 chromosomes. The genetic map lengths for each hybrid were established to compare their recombination rates.The rates were 1.4 and 2.7 times higher in the hybrids having C 6 or C 9 alone than in the control (0C). This enhancement reached 3.1 and 4.1 times in hybrids carrying six and nine C chromosomes, and it was also higher for each pair of hybrids carrying 2n = 32 or 2n = 35 chromosomes, with a dependence on which chromosomes remained as univalents.We have shown, for the first time, that the presence of one chromosome, C 9 , affects significantly the recombination rate and reduces crossover interference. This result will have fundamental implications on the regulation of crossover frequency.

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