Non-vernalization requirement in Chinese kale caused by loss of BoFLC and low expressions of its paralogs

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

doi:10.1007/s00122-021-03977-x

Qiwei Tang, Guanghui An + Show 5 more

Open Access

https://doi.org/10.1007/s00122-021-03977-x

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Abstract

Key messageWe identified the loss ofBoFLC gene as the cause of non-vernalization requirement inB. oleracea. Our developed codominant marker ofBoFLCgene can be used for breeding program ofB. oleraceacrops.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.

Highlights

Chinese kale (Brassica oleracea var. chinensis Lei) is a Brassica vegetable widely planted in Southern China and Southeast Asia (Lei et al 2017; Qian et al 2016)
We explored the genetic mechanism underlying vernalization variation in Chinese Kale and kale based on bulked segregant analysis (BSA) + RNA-seq
To genetically dissect flowering time variations between the two closely related crops, a Chinese kale cultivar was crossed with a kale cultivar (Fig. 1A), and the F 1 hybrids were selfed to generate an F2 segregating population

Summary

Introduction

Chinese kale (Brassica oleracea var. chinensis Lei) is a Brassica vegetable widely planted in Southern China and Southeast Asia (Lei et al 2017; Qian et al 2016). The stem and leaves of Chinese kale are popularly consumed owing to its flavors, vivid colors, rich anticarcinogenic and antioxidative components such as vitamin C, total phenolics, carotenoids, and glucosinolates (Sun et al 2011, 2012; Wei et al 2011; Wu et al 2017). In Arabidopsis, the vernalization pathway promotes flowering in response to extended exposure to low temperatures (Searle et al 2006). FLC encoding a MADS-box transcription factor inhibits expression of the central flowering regulator FLOWERING LOCUS T (FT) (Sheldon et al 2000). FLC binds to the promoters and represses the expressions of several other important flowering genes, such as FLOWERING LOCUS D (FD), SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1), and TEMPRANILLO 1

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