Functional Dissection Of The Flowering Regulators BnFLC.A10 And BnFTs In Brassica Napus

Flowering is a key step after thr floral transition and one of most impotant agricultural traits for crops. The floral transition is generally regulated by endogenous factors affected by environmental stimuli. Flowering in an appropriate season can allow crops to get stable and high yield. In the process of evolution and domestication, rapeseed(Brassica nupus) developed three ecotypes, spring-type, Winter-type, and semi-winter-type, to accommodate diverse climate conditions. For the canola breeders, understanding the mechanism that controls flowering is vitally important for improving crop varieties.In this studying, gene expression and transgenic analyses were used to investigate the relationship between the key genes, Bn FLC.A10 and Bn FTs, and enviromental signals in controlling flowering in B. napus. Bn FLC.A10 is the candidate underlying the major flowering time QTL in spring cropped environment. Monkey King, a MITE transposon, in Bn FLC.A10 promoter was mainly focused on its effects on gene regulation and genome evolution. Six Bn FT paralogs exist in the B. napus genome, their expression differences and roles in regulating flowering in different B. napus ecotypes were analyzed. Additionally, overexpression of Bn FTc affects plant architecture and drought resistance in transgenic rapeseed. Main results are as follow:1. Bn FLC.A10 is the candidate underlying the spring environment specific flowering time QTL found in TN-DH population which were derived from the two parents, winter rapeseed Tapidor and semi-winter rapeseed Ningyou7. When the Bn FLC.A10 allele from Tapidor was transformed into Spring rapeseed Westar, flowering had a delay in vernalization-free environments, but not in vernalization environment. In Westar, endogenous and transgene Bn FLC.A10 had a similar transcriptional level before vernalization, decreased during vernalization, and dropped to a very low level at 3 weeks after vernalization. The correspondence between the transgene transcript accumulation and the flowering phenotype explained why the QTL was only found in spring environments.2. Monkey King had no obvious impacts on Bn FLC.A10 expression and flowering time in transgenic Westar. This result seems inconsistent to our earlier report, in which Monkey King is associated with vernalization requirement in flowering in rapeseed. The Monkey King sequence within Bn FLC.A10 was methylated in transgenic Westar, which may silence its effect in regulating Bn FLC.A10 expression.3. In transgenic A. thaliana, the Monkey King element inhibited the activity of 35 S promoter when inserted upstream region of 35 S promoter. A new Monkey King insertion may enhance or repress the expression of a gene with which it is associated.4. Monkey King is a Brassicaceae Tourist MITE family and has amplified relatively recently and has induced intra- and inter-species genomic variations in Brassica. Monkey King elements are most abundant in the vicinity of genes in the B. rapa and A. thaliana genomes, and was found in many Brassica ESTs. These results suggested that Monkey King may have a substantial effect on genome-wide gene regulation in some Brassicaceae species. Additionally, Monkey King can generate Brassica specific mi RNAs.5. At the seedling stage, the transcripts of Bn FTs were observed only in leaf and cotyledon of spring rapeseed, not winter rapeseed. After cold treatment, expression of Bn FTs was also detected in winter rapeseed. When the plants were blooming, transcripts of Bn FTs were detected in all investigated tissues/organs, except root.6. Six Bn FT paralogs exist in the B. napus genome. In this studying, Bn FTs were grouped into three types: Bn FTa, Bn FTb and Bn FTc, according to the different degrees of similarity among the six Bn FT paralogs and their corresponding relationships between the A and C genomes. When we overexpressed three different types of Bn FTs in Arabidopsis, all three significantly accelerated flowering. Overexpression of Bn FTc also induced early flowering in B. napus. In particular, in winter rapeseed, overexpression of Bn FTc eliminated the vernalization requirement for flowering.7. In open field, Overexpression of Bn FTc in rapeseed changed plant architecture: apical dominace was not apparent and lateral branches were developed. Moreover, Overexpression of Bn FTc enlarged stomatal aperture and accelerated water loss, thus causing the plants more sensitive to drought.