Molecular Ecology and Evolution
Litt, Amy , Nowogrodzki, Anna , Jordan, Kevin , Franks, Steven .
The genetic basis of variation in flowering time in Brassica rapa populations.
As part of a project designed to identify the genetic basis of a change in flowering time in response to drought in two populations of Brassica rapa in southern California,we looked at sequence and expression variation in flowering time genes across a single population. Our goal was to try to identify genes with allelic variation that was correlated with flowering time, to test the hypothesis that after the drought there was an increase in the frequency of alleles that promote early flowering. To identify "early" and "late" alleles of candidate genes, we selected 10 very early and 10 very late flowering individuals and focused our sequencing efforts on orthologs of Arabidopsis FLC, FT,and SOC1. FLCis a floral repressor that functions in both the vernalization and autonomous pathways. When levels of FLC transcript drop, FT and SOC1 are upregulated and flowering is initiated. FTand SOC1 are floral integrators; all of the flowering time pathways appear to converge on these genes, the final flowering promoters. Because the flowering response depends on transcript levels, we also measured these during the course of plant growth. The Brassica rapa genome has four orthologsof FLC. We sequenced the coding region and first intron (which contains regulatory sequence) and are sequencing the promoter regions of all four genes and in no case have we found any sequence variation at all among the 10 earliest and 10 latest flowering individuals. Expression levels of FLC orthologs varied among individuals (and different genes are expressed at dramatically different levels) but these levels were not correlated with flowering time. This suggests that within these populations,the BrFLC genes do not play a significant role in determining the range of individual flowering times. In contrast, our analyses of expression of FT and SOC1 orthologs does show variation that is strongly correlated with flowering time. This confirms that the range of flowering time variation does have a genetic basis although other genes and epigenetic factors appear to playa role. BrSOC1 also shows variation in the coding sequence that is correlated with flowering time, although BrFTdoes not. Current work is focused on sequencing the promoters of these genes.
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1 - New York Botanical Garden, 200th St And Southern Blvd., Bronx, NY, 10458, USA
2 - NY Botanical Garden, Genomics, 200th St. And Southern Blvd., Bronx, NY, 10458, USA
4 - Fordham University, INVASIVE PLANT RESEARCH LAB, 441 E. Fordham Road, 160 Larkin Hall, Bronx, NY, 10458, USA
Presentation Type: Oral Paper:Papers for Topics
Location: Union B/Hyatt
Date: Monday, July 9th, 2012
Time: 2:30 PM