Abstract
In Chinese cabbage (Brassica rapa L. ssp. pekinensis), leaf adaxial-abaxial (ad-ab) polarity is tightly related to leaf incurvature, an essential factor for the formation of leafy heads. Therefore, identification of the genes responsible for leaf ad-ab polarity and studying their genetic variation may clarify the mechanism of leafy head formation. By comparing the sequences of the genes regulating leaf ad-ab polarity development in Arabidopsis thaliana (A. thaliana), 41 candidate genes distributed on 10 chromosomes were found to be responsible for the establishment of ad-ab polarity in Chinese cabbage. Orthologous genes, including 10 single copies, 14 double copies, and one triple copies, were detected in the Chinese cabbage. The gene structure and conserved domain analyses showed that the number of exons of the 41 candidate genes range from one to 25, and that most genes share the conserved motifs 1, 6, and 10. Based on the 41 candidate genes, 341 simple sequence repeats (SSRs) were detected, including five replicated types: single, double, triple, quintuple, and sextuple nucleotide replications. Among these sequence repeat (SSR) loci, 323 loci were used to design 969 specific primers, and 362 primer pairs were selected randomly and evaluated using 12 Chinese cabbage accessions with different heading types. 23 primer pairs resulting with clear, polymorphic bands, combined with other 127 markers, was used to construct a linkage map by using an F2 population containing 214 lines derived from the hybrid of the overlapping heading Chinese cabbage “14Q-141” and the outward curling heading Chinese cabbage “14Q-279.” The result showed that the sequences of markers in the genetic linkage map and the physical map was consistent in general. Our study could help to accelerate the breeding process of leafy head quality in Chinese cabbage.
Highlights
Chinese cabbage (Brassica rapa L. ssp. pekinensis) is an important leafy vegetable grown worldwide and one of the most consumed vegetables in Asia
Genes responsible for the leaf ad-ab polarity are distributed on 10 chromosomes in Chinese cabbage, with most of them (6, 14.63%) occurring on chromosome A05 and only a very few (2, 4.88%) on chromosome A01
The result showed that the sequences of markers in genetic linkage map and physical map are generally consistent, with only three groups of markers distribute in the linkage groups (LGs) A01, A05, and A08 showing different sequences (Figure 7)
Summary
Chinese cabbage (Brassica rapa L. ssp. pekinensis) is an important leafy vegetable grown worldwide and one of the most consumed vegetables in Asia. With the improvement of life quality, the leafy head appearance of Chinese cabbage is of increasing concern to both the consumers and breeders (Mao et al, 2014; Liang et al, 2016). Chinese cabbage goes through three developmental stages to produce a leafy head, namely, seedling, rosette, and heading (Yu et al, 2013). Leaf incurvature is influenced by leaf ad-ab polarity, and is a precondition for the formation of leafy heads (Mao et al, 2014; Liang et al, 2016). Studies on leaf ad-ab polarity is helpful for improving the commercial traits of Chinese cabbage (Yu et al, 2013; Mao et al, 2014)
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