PLANT OF THE DAY Paris japonica (native of Japan) Family Melanthaceae Largest Eukaryotic genome 150 Gbp DNA from a single cell stretched out end-to-end would be taller than 300 feet (91 m)
PLANT OF THE DAY Paris japonica (native of Japan) Largest plant genome known to science 150 Gbp Oak circa 0.9 Gb Paris japonica
oak Big Questions Why do genome sizes vary wildly among organisms with similar levels of cellular and developmental complexity (the C-Value paradox)?
What is the function and evolutionary role of repetitive elements? C-Value Paradox Why do genome sizes vary wildly among organisms with similar levels of cellular and developmental complexity?
Percent of DNA non-coding C-Value Paradox Why does the percent of non-coding DNA vary wildly among organisms with similar levels of cellular and developmental complexity? Hypotheses:
1)Selfish DNA most non-coding DNA consists for selfish elements capable of proliferating until the cost to host fitness becomes prohibitive. 2)Bulk DNA genome size has a direct effect on nuclear volume, cell size, and cell division rate, all of which influence important life history features. 3)Metabolic cost of DNA limits genome size.
4)Interspecific variation in mutational tendency to delete excess DNA. 5)Population size and mutational hazard of excess DNA, especially gain of function mutations. 6)All of the above genome,size,
and large Ne LargeLarge genome small Ne
Mike Lynch Phylogenetically independent contrasts Ken Whitney
Plant Nuclear Genome Size Variation 7058 species surveyed and databased ~ 2300X difference 63 mbp 150,000 mbp
Genlisea margaretae http://data.kew.org/cvalues/ A ROLE FOR NONADAPTIVE PROCESSES IN PLANT GENOME SIZE EVOLUTION? Evolution Volume 64, Issue 7, pages 2097-2109, 9 FEB 2010
Chromosome Number Variation Chromosome numbers vary n = 2 to n = ~680 Euploid variation polyploidy ~35% of vascular plants are neopolyploids All are paleopolyploids
Aneuploid variation gain or less of one or more chromosomes Post polyploid genome size change is variable -Additive sum of parents -Increase
-Decrease Correlation of Chromosome Number and Genome Size Angiosperm r = -0.023 Gymnosperm r = 0.106 Pteridophytes r = 0.913
Variation in the number of nuclear genes Plant Nuclear Gene Overlap ~90% of genes have homologs in other genomes Does not appear to be large differences most genomes around 40,000
Not a substantial contributor to variation in genome size Transposable Elements (TEs) 50-80% of plant genomes are TEs Discovered by Barbara McClintock by studying unstable corn kernel
phenotypes Fragments of DNA that can insert into new chromosomal locations Often duplicate themselves during the process of moving around Class 1 TEs use RNA intermediates to move around and undergo duplicative
transposition Class 2 TEs are excised during transposition and may undergo cut and paste transposition with no duplication or gap repair where the gap is filled with a copy of the transposon Autonomous elements contain necessary genes for transposition Non-autonomous elements rely on products of other elements for transposition
MITES: Miniature Inverted Repeat Transposable Elements Class 2 elements found in or near genes A few dozen to few hundred base pairs in length Two inverted repeats
Non-autonomous activated by other autonomous TEs 6% of Arabidopsis and 12% of rice genomes are composed of MITES LTRs: Long Terminal Repeat Retrotransposons
Class 1 elements found between genes Autonomous self activating Duplicative transposition Single largest component of plant genomes 50-70% of maize genome is LTR
LTR Driven Genome Expansion in Maize 240 KB contig containing adh1 ~60% of sequence was retrotransposon Copy numbers 10 1000
Comparison to syntetic region in Sorghum showed no evidence of transposons Dating suggest doubling of maize genome in less than 6 million years Rate of Transposable Element Insertion and Fitness Effects
Average reductions in fitness per insertion: 0.5 -1.5% Are genome size and TE growth unchecked? Ages of LTRs in Rice Bursts of LTR
expansion Hopi is currently active and accounts for 30% of rice genome Half life of ~3 MYR By examining the number of truncated
LTRs, it appears that 61-78% of the DNA has been removed since insertion in the last 5 MYR Boom & Bust Cycle Fueled by Hybridization & Stress
Data do not suggest stabilization -no old TEs -TEs demonstrate boom/bust patterns TEs proliferate in nave hosts (hybridization) Stress overwhelms host ability to limit TEs
Why is aneuploidy more common in flowering plants than ferns? What is the role of TEs in adaptive evolution? Is the proliferation of TEs following genomic stress adaptive or is it a maladaptive consequence of the breakdown of mechanisms that suppress TE amplification? What is the metabolic cost of synthesizing DNA?
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