Abstract Detail

Molecular Ecology and Evolution

McAssey, Edward [1], Burke, John [1].

Differential expression and molecular evolution of genes expressed in an adaptive trait: Developing wild sunflower seeds.

Variation in the fatty acid content of seeds is a recurring pattern seen across many groups of angiosperms. Both theory and reciprocal transplant experiments in the genus Helianthus have shown that populations from northern latitudes tend to have lower amounts of saturated fatty acids than southern populations and accordingly have higher fitness in their home environment. In contrast, southern populations have a fitness advantage in their home environment. It has been hypothesized that the differential melting points of various fatty acids are responsible for these fitness trends. Specifically, high energy saturated fatty acids have higher melting points and thus would be difficult to use for northern populations. In contrast, relatively lower energy unsaturated fatty acids have lower melting points and thus are exploitable at lower temperatures typically seen in northern latitudes. Although this pattern and its resulting fitness consequences are known, we know very little about the genetic basis of the intraspecific variation. We sought to determine the genetic basis of fatty acid variation by sequencing transcriptomes from 20 common garden grown wild sunflowers from both Texas and Canada. We performed a de novo transcriptome assembly using the Trinity pipeline. We then performed a differential expression analysis using RSEM and EdgeR. Multi-dimensional scaling shows general latitudinal differentiation in gene expression patterns. Furthermore, hundreds of isoforms were differentially expressed between northern and southern populations. We analyzed our differentially expressed isoforms by asking two general questions: 1) are homologs of known fatty acid biosynthesis genes from Arabidopsis thaliana differentially expressed in wild sunflower and 2) are significantly differentiated isoforms in wild sunflower found in quantitative trait locus intervals for seed related traits? By mapping individual libraries back to the assembly we found that there is a SNP approximately every 256 base pairs. Our analysis of differential expression shows that four homologs of A. thaliana fatty acid biosynthesis genes are differentially expressed when comparing northern and southern individuals although no fatty acid desaturases were differentially expressed. Differentially expressed genes were also found to co-localize with QTL for fatty acid biosynthesis and seed architecture traits. Additionally, we considered the relative abundance of synonymous and non-synonymous mutations of both differentially expressed and non-differentially expressed genes to detect whether differentially expressed genes were on average more functionally constrained in order to determine the roles of regulatory and structural mutations in local adaptation.

1 - University Of Georgia, Plant Biology, 2502 Miller Plant Sciences, Athens, GA, 30602, USA

Keywords:
sunflower
local adaptation
transcriptomics
seed
Fatty acid.

Presentation Type: Oral Paper:Papers for Topics
Session: 61
Location: Salon 15/16/The Shaw Conference Centre
Date: Wednesday, July 29th, 2015
Time: 10:15 AM
Number: 61009
Abstract ID:959
Candidate for Awards:Margaret Menzel Award