Abstract Detail



Hybrids and Hybridization

McCarthy, Elizabeth [1], Landis, Jacob [2], Kurti, Amelda [3], Lawhorn, Amber [3], Litt, Amy [4].

The genetic basis of flower color differences in Nicotiana tabacum.

Allopolyploidy involves both whole genome duplication and interspecific hybridization.  This merger of divergent genomes within the same nucleus results in genomic shock, which induces changes in gene expression, chromosome rearrangements, transposable element activation, and physiological and morphological changes.  These morphological changes can manifest as a diversity of phenotypes in allopolyploids from a single origin.  We are interested in elucidating the genetic changes that underlie the diversity of phenotypes in allopolyploids.  To address this, we use Nicotiana (tobacco) allopolyploids that share the same origin and/or progenitors.  We examined magenta- and light pink-flowered accessions of Nicotiana tabacum, which arose approximately 0.6 million years ago from N. sylvestris (white-flowered) and N. tomentosiformis (dark pink-flowered) progenitors, as well as light pink- and dark pink-flowered first-generation synthetic allopolyploid lines from a cross between the same progenitor species.  Differences in pink hue among these accessions are due to increased cyanidin concentration in darker pink flowers.  Cyanidin pigments are produced by the flavonoid biosynthetic pathway, a branched pathway that creates both colorful anthocyanin and colorless (to humans) flavonol pigments.  To determine the gene expression changes that underlie differences in floral color, we sequenced transcriptomes from corolla tissue of floral buds at 60%, 85%, and 95% of anthesis length from the two natural accessions and the two synthetic lines described above as well as their diploid progenitors.  We analyzed transcript levels of the structural and regulatory genes known to be involved in the flavonoid biosynthetic pathway.  The ratio between FLAVONOL SYNTHASE (FLS), which creates flavonols, and DIHYDROFLAVONOL 4-REDUCTASE (DFR), which begins the synthesis of anthocyanins, is high in light pink flowers early in floral development (60% of anthesis length buds).  FLS and DFR act on the same substrates; therefore, this high FLS:DFR ratio suggests that competition between these enzymes may result in making flavonols at the expense of making anthocyanins, thus creating a light pink flower.  This high FLS:DFR ratio seems to be due to delayed activation of DFR expression in light pink flowers compared to dark pink flowers.  Thus, the diversity of floral color phenotypes in related Nicotiana allopolyploids seems to be due to changes in the developmental timing of expression of the genes that produce anthocyanins, leading to differences in the outcome of competition for the same substrates, which results in diverse flower colors.


1 - University Of California, Riverside, Department Of Botany And Plant Sciences, 900 University Ave., Riverside, CA, 92521, United States
2 - University Of California Riverside, Botany And Plant Sciences, 3401 Watkins Drive, Boyce Hall, Room 4412, Riverside, CA, 92507, United States
3 - University of California, Riverside, Botany and Plant Sciences, 900 University Ave., Riverside, CA, 92521, USA
4 - University Of California, Riverside, Botany And Plant Sciences, 900 University Avenue, Riverside, CA, 92521, United States

Keywords:
allopolyploidy
Anthocyanin
Evolution
flower color
Nicotiana.

Presentation Type: Oral Paper
Number: 0002
Abstract ID:281
Candidate for Awards:Margaret Menzel Award


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