Abstract Detail

Hybrids and Hybridization

McCarthy, Elizabeth [1], Berardi, Andrea [2], Smith, Stacey D. [3], Litt, Amy [4].

Diverse and novel phenotypes in allopolyploids: floral pigments and their genetic basis.

Polyploidy, or whole genome duplication (WGD), is a widespread phenomenon in the evolution of flowering plants. Allopolyploidy involves WGD and interspecific hybridization, and the merger of distinct genomes can result in genetic and epigenetic changes, including differential gene expression, transposon activity, and chromosomal rearrangements. Allopolyploids often display diverse and even transgressive (outside the range of the progenitors) phenotypes. These phenotypes may be due to novel regulatory interactions between progenitor genomes as they come together within the same nucleus. Here, we investigate the genetic and regulatory basis for the diverse and transgressive floral color phenotypes found in allopolyploids. Floral color affects pollinator attraction and thus floral color differences may lead to reproductive isolation and species diversification.
In the genus Nicotiana (tobacco), approximately half the species are allotetraploids of different ages. The diploid progenitors of these polyploids have been well-established. Nicotiana displays substantial diversity in floral morphology, and allopolyploids from the same progenitors often have divergent floral phenotypes. Using two accessions of N. tabacum that display different floral colors (magenta and pink), we tested the hypothesis that differences in homeolog (progenitor gene copy) expression ratios underlie floral color variation in allopolyploids. To address this hypothesis, we quantified pigment gene expression from transcriptome data and measured the composition and concentration of floral flavonoids (anthocyanins and flavonols). The flavonoid biosynthetic pathway produces multiple types of pigments, and variation in regulation of this pathway yields different floral colors. We mapped our pigment data and homeolog expression ratios onto the pathway to determine whether differential homeolog expression between two accessions of the same allopolyploid species yields different pigment composition or concentration. Magenta N. tabacum flowers have an increased concentration of cyanidin pigment compared to pink N. tabacum flowers. However, at anthesis, there are no differences in homeolog expression ratios or overall expression of anthocyanin biosynthetic genes, which does not support our hypothesis. It is possible that differential expression earlier in floral development yields floral color differences. Based on preliminary semi-quantitative RT-PCR data, late anthocyanin biosynthetic genes seem to be upregulated earlier in development in magenta flowers, suggesting production of cyanidin over a longer period, which may explain the observed increase in concentration. In addition, Nicotiana allopolyploids produce novel pigments not observed in either of their progenitors, suggesting that allopolyploidy yields shifts in the regulation and flux of the flavonoid biosynthetic pathway that create transgressive phenotypes, which may affect pollinator attraction.

1 - University of California, Riverside, Department of Botany and Plant Sciences, 900 University Ave., Riverside, CA, 92521, USA
2 - University Of Colorado - Boulder, Department Of Ecology And Evolutionary Biology, C127 Ramaley Hall, University Of Colorado-Boulder Campus Box 334, P.O. Box 400328, Boulder, CO, 80309, USA
3 - University Of Colorado-Boulder, School Of Biological Sciences, Campus Box 334, Boulder, CO, 80309-0334, USA
4 - University of California, Riverside, 900 University Avenue, Riverside, CA, 92521, United States

Keywords:
polyploidy
hybridization
flower color
anthocyanin
Nicotiana.

Presentation Type: Oral Paper
Session: 50, Hybrids and Hybridization
Location: 102/Savannah International Trade and Convention Center
Date: Wednesday, August 3rd, 2016
Time: 4:30 PM
Number: 50004
Abstract ID:296
Candidate for Awards:Margaret Menzel Award