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Clubroot disease caused by Plasmodiophora brassicae is one of the major threats to Brassica crops. New clubroot resistant varieties of Chinese cabbage (B. rapa ssp. pekinensis) have been developed through breeding, but the underlying genetic mechanism of clubroot resistance is still unclear. In this study, two Chinese cabbage DH lines, clubroot-resistant Y635-10 and susceptible Y177-47 were crossed to develop F2 population for fine mapping and cloning resistance gene CRq. After sequence analysis, the expression vector was constructed by gateway technology and transferred into Arabidopsis thaliana for functional characterization. Bulked segregant analysis sequencing (BSA-seq) confirmed that CRq is located in the 80 kb genomic region on chromosome A03 between markers GC30-FW/RV and BGA. In silico tools confirmed that the gene length was 3959 bp with 3675 bp coding sequences (CDs), and it has three exons and two introns. In addition, we found 72bp insertion in the third exon of CRq in the susceptible line. We developed and verified functional marker Br-insert1, by which genotyping results showed that 72bp insertion might lead to the destruction of the LRR region of Y177-47, resulting in a loss of resistance relative to clubroot. The results of genetic transformation showed that the roots for wild-type Arabidopsis thaliana were significantly enlarged compared with T2 generation transgenic Arabidopsis after treatment by P. brassicae spores, and transgenic Arabidopsis had certain resistance. Therefore, CRq is a candidate gene of clubroot disease resistance in Chinese cabbage, which could be used as a reference for elucidating disease resistance mechanisms and the marker-assisted breeding of clubroot resistant varieties.

Chinese cabbage (Brassica rapa L.) is one of the most important and highly nutritious vegetables in China belonging to the Brassicaceae family. Flowering or bolting is one of the most critical developmental stages in flowering plants. For the spring-sown Chinese cabbage, late-bolting is desirable over early-bolting according to consumer preferences. We determined the inheritance pattern of the late-bolting trait using F1 and F2 generated from a cross between ‘SY2004’ (late-bolting) and ‘CX14-1’ (early-bolting). The genetic analysis revealed that the late-bolting to early-bolting trait was controlled by an incomplete dominant gene that we named BrLb-1. Furthermore, we performed bulked segregant analysis (BSA) via whole genome re-sequencing and the results showed that this gene was harbored on the chromosome A07 at the intersections of 20,070,000 to 25,290,000 bp and 20,330,000 to 25,220,000, an interval distance of 4.89 Mb. In this candidate interval, totals of 2321 and 1526 SNPs with non-synonymous mutations, and 229 and 131 InDels with frameshift mutations, were found between the parents and the bulked pools, respectively. Furthermore, we identified three putative candidate genes for the late-bolting trait, including BraA07g029500, BraA07g029530 and BraA07g030360, which code for the AGAMOUS-like MADS-box protein AGL12, a pentatricopeptide repeat-containing protein and NAC transcription factor 29, respectively; however, further functional analysis is required. These genetic variants could be utilized for the further development of molecular markers for marker-assisted breeding in Chinese cabbage.