Dataset Information

The Brassica rapa FLC homologue FLC2 is a key regulator of flowering time, identified through transcriptional co-expression networks.

ABSTRACT: The role of many genes and interactions among genes involved in flowering time have been studied extensively in Arabidopsis, and the purpose of this study was to investigate how effectively results obtained with the model species Arabidopsis can be applied to the Brassicacea with often larger and more complex genomes. Brassica rapa represents a very close relative, with its triplicated genome, with subgenomes having evolved by genome fractionation. The question of whether this genome fractionation is a random process, or whether specific genes are preferentially retained, such as flowering time (Ft) genes that play a role in the extreme morphological variation within the B. rapa species (displayed by the diverse morphotypes), is addressed. Data are presented showing that indeed Ft genes are preferentially retained, so the next intriguing question is whether these different orthologues of Arabidopsis Ft genes play similar roles compared with Arabidopsis, and what is the role of these different orthologues in B. rapa. Using a genetical-genomics approach, co-location of flowering quantitative trait loci (QTLs) and expression QTLs (eQTLs) resulted in identification of candidate genes for flowering QTLs and visualization of co-expression networks of Ft genes and flowering time. A major flowering QTL on A02 at the BrFLC2 locus co-localized with cis eQTLs for BrFLC2, BrSSR1, and BrTCP11, and trans eQTLs for the photoperiod gene BrCO and two paralogues of the floral integrator genes BrSOC1 and BrFT. It is concluded that the BrFLC2 Ft gene is a major regulator of flowering time in the studied doubled haploid population.

SUBMITTER: Xiao D

PROVIDER: S-EPMC3808329 | biostudies-literature | 2013 Nov

REPOSITORIES: biostudies-literature

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The Brassica rapa FLC homologue FLC2 is a key regulator of flowering time, identified through transcriptional co-expression networks.

Xiao Dong D Zhao Jian J JJ Hou Xi L XL Basnet Ram K RK Carpio Dunia P D DP Zhang Ning W NW Bucher Johan J Lin Ke K Cheng Feng F Wang Xiao W XW Bonnema Guusje G

Journal of experimental botany 20130927 14

The role of many genes and interactions among genes involved in flowering time have been studied extensively in Arabidopsis, and the purpose of this study was to investigate how effectively results obtained with the model species Arabidopsis can be applied to the Brassicacea with often larger and more complex genomes. Brassica rapa represents a very close relative, with its triplicated genome, with subgenomes having evolved by genome fractionation. The question of whether this genome fractionati ...[more]

PMID: 24078668

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Project description:Background:Brassica rapa is an important oilseed and vegetable crop species and is the A subgenome donor of two important oilseed Brassica crops, Brassica napus and Brassica juncea. Although seed size (SZ), seed color (SC), and oil content (OC) substantially affect seed yield and quality, the mechanisms regulating these traits in Brassica crops remain unclear. Results:We collected seeds from a pair of B. rapa accessions with significantly different SZ, SC, and OC at seven seed developmental stages (every 7 days from 7 to 49 days after pollination), and identified 28,954 differentially expressed genes (DEGs) from seven pairwise comparisons between accessions at each developmental stage. K-means clustering identified a group of cell cycle-related genes closely connected to variation in SZ of B. rapa. A weighted correlation analysis using the WGCNA package in R revealed two important co-expression modules comprising genes whose expression was positively correlated with SZ increase and negatively correlated with seed yellowness, respectively. Upregulated expression of cell cycle-related genes in one module was important for the G2/M cell cycle transition, and the transcription factor Bra.A05TSO1 seemed to positively stimulate the expression of two CYCB1;2 genes to promote seed development. In the second module, a conserved complex regulated by the transcription factor TT8 appear to determine SC through downregulation of TT8 and its target genes TT3, TT18, and ANR. In the third module, WRI1 and FUS3 were conserved to increase the seed OC, and Bra.A03GRF5 was revealed as a key transcription factor on lipid biosynthesis. Further, upregulation of genes involved in triacylglycerol biosynthesis and storage in the seed oil body may increase OC. We further validated the accuracy of the transcriptome data by quantitative real-time PCR of 15 DEGs. Finally, we used our results to construct detailed models to clarify the regulatory mechanisms underlying variations in SZ, SC, and OC in B. rapa. Conclusions:This study provides insight into the regulatory mechanisms underlying the variations of SZ, SC, and OC in plants based on transcriptome comparison. The findings hold great promise for improving seed yield, quality and OC through genetic engineering of critical genes in future molecular breeding.

Project description:Understanding the genetic basis of natural phenotypic variation is of great importance, particularly since selection can act on this variation to cause evolution. We examined expression and allelic variation in candidate flowering time loci in Brassica rapa plants derived from a natural population and showing a broad range in the timing of first flowering. The loci of interest were orthologs of the Arabidopsis genes FLC and SOC1 (BrFLC and BrSOC1, respectively), which in Arabidopsis play a central role in the flowering time regulatory network, with FLC repressing and SOC1 promoting flowering. In B. rapa, there are four copies of FLC and three of SOC1. Plants were grown in controlled conditions in the lab. Comparisons were made between plants that flowered the earliest and latest, with the difference in average flowering time between these groups ∼30 days. As expected, we found that total expression of BrSOC1 paralogs was significantly greater in early than in late flowering plants. Paralog-specific primers showed that expression was greater in early flowering plants in the BrSOC1 paralogs Br004928, Br00393 and Br009324, although the difference was not significant in Br009324. Thus expression of at least 2 of the 3 BrSOC1 orthologs is consistent with their predicted role in flowering time in this natural population. Sequences of the promoter regions of the BrSOC1 orthologs were variable, but there was no association between allelic variation at these loci and flowering time variation. For the BrFLC orthologs, expression varied over time, but did not differ between the early and late flowering plants. The coding regions, promoter regions and introns of these genes were generally invariant. Thus the BrFLC orthologs do not appear to influence flowering time in this population. Overall, the results suggest that even for a trait like flowering time that is controlled by a very well described genetic regulatory network, understanding the underlying genetic basis of natural variation in such a quantitative trait is challenging.

Project description:Orphan genes are essential to the emergence of species-specific traits and the process of evolution, lacking sequence similarity to any other identified genes. As they lack recognizable domains or functional motifs, however, efforts to characterize these orphan genes are often difficult. Flowering is a key trait in Brassica rapa, as premature bolting can have a pronounced adverse impact on plant quality and yield. Bolting resistance-related orphan genes, however, have yet to be characterized. In this study, an orphan gene designated BOLTING RESISTANCE 1 (BR1) was identified and found through gene structural variation analyses to be more highly conserved in Chinese cabbage than in other available accessions. The expression of BR1 was increased in bolting resistant Chinese cabbage and decreased in bolting non-resistant type, and the expression of some mark genes were consist with bolting resistance phenotype. BR1 is primarily expressed in leaves at the vegetative growth stage, and the highest BR1 expression levels during the flowering stage were observed in the flower buds and silique as compared to other tissue types. The overexpression of BR1 in Arabidopsis was associated with enhanced bolting resistance under long day (LD) conditions, with these transgenic plants exhibiting significant decreases in stem height, rosette radius, and chlorophyll content. Transcriptomic sequencing of WT and BR1OE plants showed the association of BR1 with other bolting resistance genes. Transcriptomic sequencing and qPCR revealed that six flowering integrator genes and one chlorophyll biosynthesis-related gene were downregulated following BR1 overexpression. Six key genes in photoperiodic flowering pathway exhibited downward expression trends in BR1OE plants, while the expression of floral repressor AtFLC gene was upregulated. The transcripts of these key genes were consistent with observed phenotypes in BR1OE plants, and the results indicated that BR1 may function through vernalization and photoperiodic pathway. Instead, the protein encoded by BR1 gene was subsequently found to localize to the nucleus. Taken together, we first propose that orphan gene BR1 functions as a novel regulator of flowering time, and these results suggested that BR1 may represent a promising candidate gene to support the selective breeding of Chinese cabbage cultivars with enhanced bolting resistance.

Dataset Information

The Brassica rapa FLC homologue FLC2 is a key regulator of flowering time, identified through transcriptional co-expression networks.

Publications

The Brassica rapa FLC homologue FLC2 is a key regulator of flowering time, identified through transcriptional co-expression networks.

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