Abstract
BackgroundRapeseed (Brassica napus L.) has spring and winter genotypes adapted to different growing seasons. Winter genotypes do not flower before the onset of winter, thus leading to a longer vegetative growth period that promotes the accumulation and allocation of more resources to seed production. The development of winter genotypes enabled the rapeseed to spread rapidly from southern to northern Europe and other temperate regions of the world. The molecular basis underlying the evolutionary transition from spring- to winter- type rapeseed is not known, however, and needs to be elucidated.ResultsWe fine-mapped the spring environment specific quantitative trait locus (QTL) for flowering time, qFT10-4,in a doubled haploid (DH) mapping population of rapeseed derived from a cross between Tapidor (winter-type) and Ningyou7 (semi-winter) and delimited the qFT10-4 to an 80-kb region on chromosome A10 of B. napus. The BnFLC.A10 gene, an ortholog of FLOWERING LOCUS C (FLC) in Arabidopsis, was cloned from the QTL. We identified 12 polymorphic sites between BnFLC.A10 parental alleles of the TN-DH population in the upstream region and in intron 1. Expression of both BnFLC.A10 alleles decreased during vernalization, but decreased more slowly in the winter parent Tapidor. Haplotyping and association analysis showed that one of the polymorphic sites upstream of BnFLC.A10 is strongly associated with the vernalization requirement of rapeseed (r2 = 0.93, χ2 = 0.50). This polymorphic site is derived from a Tourist-like miniature inverted-repeat transposable element (MITE) insertion/deletion in the upstream region of BnFLC.A10. The MITE sequence was not present in the BnFLC.A10 gene in spring-type rapeseed, nor in ancestral ‘A’ genome species B. rapa genotypes. Our results suggest that the insertion may have occurred in winter rapeseed after B. napus speciation.ConclusionsOur findings strongly suggest that (i) BnFLC.A10 is the gene underlying qFT10-4, the QTL for phenotypic diversity of flowering time in the TN-DH population, (ii) the allelic diversity caused by MITE insertion/deletion upstream of BnFLC.A10 is one of the major causes of differentiation of winter and spring genotypes in rapeseed and (iii) winter rapeseed has evolved from spring genotypes through selection pressure at the BnFLC.A10 locus, enabling expanded cultivation of rapeseed along the route of Brassica domestication.
Highlights
Rapeseed (Brassica napus L.) has spring and winter genotypes adapted to different growing seasons
Eight recombinants were identified and the quantitative trait locus (QTL) qFT10-4 was delimited to an 80-kb region that showed collinearity with the top of chromosome 5 of Arabidopsis thaliana (Figure 1B and C)
We demonstrated for the first time that flowering time variation at the qFT.10-4 locus is conditioned by the major vernalization response gene, BnFLC
Summary
Rapeseed (Brassica napus L.) has spring and winter genotypes adapted to different growing seasons. The molecular basis underlying the evolutionary transition from spring- to winter- type rapeseed is not known, and needs to be elucidated. Interaction between various environmental signals and flowering genes is critical for plants to flower and complete their life cycle, and important to humans, who rely upon adequate production of fruit and seeds to feed the world’s growing population. Climate change fluctuations accompanying global warming [1,2] are requiring plant breeders to elucidate the molecular mechanisms underlying flowering, and to develop strategies for manipulating and optimizing the flowering times to maximize crop yields. Vernalization is an adaptive trait in which plants acquire the ability to flower following exposure to cold temperatures. FLC expression has been shown to be regulated via histone acetylation and methylation, which alters the expression of a trans-acting regulator common to FLC and members of the related MADS AFFECTING FLOWERING gene [17,18,19,20]
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