Abstract Detail

Hybrids and Hybridization

McCoy, Abigail G. [1], Landis, Jacob [2], McCarthy, Elizabeth [3].

Are signatures of positive selection present at flower color shifts in Nicotiana?

Pollinators have been driving the evolution of angiosperms for millions of years. Different pollinators can facilitate speciation due to their attraction to different colored flowers. Variation in flower color results from the presence of different pigments, including those produced by the flavonoid biosynthetic pathway. This branched pathway creates various flavonols, which are colorless to humans, and anthocyanins of different hues, including pelargonidin (red), cyanidin (magenta), and delphinidin (purple). Mutations in the coding sequences of the enzymes of this branched pathway can alter both their affinity for substrates and their efficiency, which will affect the pigment composition produced. The objective of this study is to identify the evolutionary pressures acting on the genes of the flavonoid biosynthetic pathway and how these pressures may have affected flower color shifts in the genus Nicotiana (Solanaceae), which exhibits striking variation in flower color. We hypothesize that positive selection will correlate with floral pigment shifts between 1) the species that produce anthocyanins versus those that do not and 2) the species producing cyanidin versus delphinidin. To determine this, we obtained available transcriptome data and extracted the sequences of flavonoid biosynthetic pathway genes to run nonsynonymous to synonymous mutation ratio (dN/dS) analyses. The values of the ratio will indicate which evolutionary pressure has acted on the flavonoid biosynthetic genes. If the dN/dS ratio is greater than one, then we can conclude that positive selection occurred. A ratio value equal to one shows that these genes were acted on by neutral evolution. Both of these pressures may alter the protein sequence, potentially changing its function. However, a ratio value less than one will indicate purifying selection, which maintains the protein sequence and its current function. Our results will indicate whether changes in coding sequence, affecting the affinity and efficiency of the enzymes in the flavonoid biosynthetic pathway, have played a role in the evolution of flower color in the genus Nicotiana. These results, together with gene expression analyses and simulations of flavonoid biosynthetic pathway evolution, will provide insight into the genetic and biochemical bases of flower color shifts among Nicotiana species.

1 - SUNY Cortland, Department of Biological Sciences, P.O. Box 2000, Cortland, NY, 13045, US
2 - Cornell University
3 - SUNY Cortland, Department Of Biological Sciences, P.O. Box 2000, Cortland, NY, 13045, United States

dN/dS analysis
Flower color

Presentation Type: Oral Paper
Number: HH1006
Abstract ID:885
Candidate for Awards:None

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