Qiwei Tang, Hanhui Kuang, Changchun Yu, Guanghui An, Rong Tao, Weiyi Zhang & Yue Jia

Theoretical and Applied Genetics; February 2022; vol. 135: 473–483

Key message

We identified the loss of BoFLC gene as the cause of non-vernalization requirement in B. oleracea. Our developed codominant marker of BoFLC gene can be used for breeding program of B. oleracea crops.

Abstract

Many species of the Brassicaceae family, including some Brassica crops, require vernalization to avoid pre-winter flowering. Vernalization is an unfavorable trait for Chinese kale (Brassica oleracea var. chinensis Lei), a stem vegetable, and therefore it has been lost during its domestication/breeding process. To reveal the genetics of vernalization variation, we constructed an F₂ population through crossing a Chinese kale (a non-vernalization crop) with a kale (a vernalization crop). Using bulked segregant analysis (BSA) and RNA-seq, we identified one major quantitative trait locus (QTL) controlling vernalization and fine-mapped it to a region spanning 80 kb. Synteny analysis and PCR-based sequencing results revealed that compared to that of the kale parent, the candidate region of the Chinese kale parent lost a 9,325-bp fragment containing FLC homolog (BoFLC). In addition to the BoFLC gene, there are four other FLC homologs in the genome of B. oleracea, including Bo3g005470, Bo3g024250, Bo9g173370, and Bo9g173400. The qPCR analysis showed that the BoFLC had the highest expression among the five members of the FLC family. Considering the low expression levels of the four paralogs of BoFLC, we speculate that its paralogs cannot compensate the function of the lost BoFLC, therefore the presence/absence (PA) polymorphism of BoFLC determines the vernalization variation. Based on the PA polymorphism of BoFLC, we designed a codominant marker for the vernalization trait, which can be used for breeding programs of B. oleracea crops.

See: https://link.springer.com/article/10.1007/s00122-021-03977-x

Figure 1: Genetic mapping of genes affecting flowering time. A Parents used for constructing the F₂ population. Kale, left panel; Chinese kale, right panel. Bar = 2 cm. B Flowering individual and non-flowering individual in an F₄ family. Bar = 2 cm. C Plot of SNP-index along 9 chromosomes of cabbage. The x-axis represents the nine chromosomes and the y-axis represents the average SNP-index in each sliding window. The red curves represent statistical confidence intervals under the null hypothesis of no QTL at p < 0.05. D Fine mapping of KVG1. The numbers below the horizontal line and between two markers refer to the number of recombinants from 587 individuals.