Molecular Systematics of Plants
Department of Biological Sciences, University of Illinois at Chicago
I am an evolutionary biologist studying the phylogenetic history of plants. I am especially interested in the complex reticulate patterns that arise when distinct lineages undergo gene exchange. The grass family includes many examples of reticulate evolution, involving hybridization and allopolyploidy.
analyses of Triticeae, the wheat tribe, reveal a history of
reticulation among diploids and polyploids. Early molecular studies
showed phylogenetic conflict among molecular data sets even when only
diploids were included. Currently we are applying targeted sequence
capture of low-copy protein-coding loci to a broad sample of diploid
taxa to determine whether conflicting phylogenetic signal is localized
the genome, or broadly distributed throughout.
wheat tribe includes many examples of hybridization and
allopolyploidy. The St
genome of Pseudoroegneria
inclined to join other genomes in a
variety of allopolyploid combinations. Elymus
an entirely allopolyploid genus, comprising several
different combinations of parental genome donors, but they all share at
least one set of Pseudoroegneria (bluebunch wheatgrass)
which are designated St.
Native North American Elymus species are allotetraploid, combining the Pseudoroegneria genome with that of Hordeum (H; wild barley) in an StStHH configuration. Phylogenetic analyses of North American Elymus based on DNA sequence data from the chloroplast genome, and from nuclear genes encoding starch synthase, phosphoenolpyruvate carboxylase, and beta-amylase, confirm the StStHH genome complement. They further reveal introgression from and Asian Pseudoroegneria species into North American Pseudoroegneria and Elymus.
We have analyzed Eurasion StStHH Elymus species
to determine whether the St and H genomes of
Eurasion species are distinct from those of the North American species,
which would indicate separate origins of StStHH tetraploids.
The phylogenetic data to date, based on phosphoenolpyruvate carboxylase, beta-amylase, and starch synthase gene trees suggest a single, North American
origin for the the Eurasian and North American StStHH tetraploids.
The Y genome of the Asian StStYY
tetraploid species is derived from an unknown donor (which
or may not be extant). Phylogenetic analyses of the phosphoenolpyruvate carboxylase, beta-amylase, and starch synthase gene sequences confirm that the St and Y genomes represent distinct evolutionary lineages, and further show that St genes have been acquired from multiple Pseudoroegneria species.
Europe and Asia is now
throughout the United States. Its phylogenetic affinities within
the Triticeae are poorly understood, but earlier cytogenetic studies suggest that it is derived from Pseudoroegneria (St genome) and Hordeum (H genome), resulting in an StStStStHH hexaploid. I have been using
data from the chloroplast genome and three nuclear genes (granule-bound starch synthase I, beta-amylase and
phosphoenolpyruvate carboxylase) to clarify its relationships to the diploid
of the tribe. Together, the
indicate a complex origin of this enigmatic allohexaploid
Chloroplast DNA - a Pseudoroegneria donor. Results from this maternally-inherited genome suggests that Pseudoroegneria was one of the genome donors to E. repens. (Most St-containing polyploids examined to date have a Pseudoroegneria-like chloroplast genome.) cpDNA tree.
Nuclear genes - three genome donors. The placement of E. repens sequences on the nuclear genes trees is partially consistent with the cytogenetic studies; they show that Pseudoroegneria and Hordeum
were genome donors. In addition, however, they all show that a third
distinct donor, currently unidentified, was involved in the origin of
the hexaploid. Nuclear trees.
Introgression involving the starch synthase gene. In addition to the Pseudoroegneria, Hordeum, and unknown-donor gene copies seen on all three trees, Elymus repens has two additional starch synthase copies. One is nearly identical to another introduced weedy species, Taeniatherum caput-medusae,
and the other is derived from the Poeae-Aveneae clade outside of the
Triticeae. Because these are unique to one gene tree, they are
interpreted as products of introgression. GBSSI trees.
Reticulation and speciation in Coreopsis
Introgression of the chloroplast genome - C. grandiflora. My previous analyses of chloroplast DNA diversity in C. grandiflora reveal that the species is split by a deep polymorphism, representing either lineage sorting or introgression. The polymorphism transcends not only the boundaries of the species, but those of section Coreopsis as well. The distribution of the polymorphism corresponds better to geographic distribution than to varietal identity. However, because the pattern of cpDNA diversity is strongly dominated by variation that predates the species's origin, additional data from nuclear genes are needed to address whether the C. grandiflora is undergoing allopatric speciation.
Rapid speciation - C. nucensoides and C. nuecensis. These species are narrowly distributed in adjacent ranges. They are intersterile and differ in chromosome number, and C. nuecensis is hypothesized to have airsen from C. nuecensoidesthrough rapid speciation associated with the sterility barrier. Chloroplast DNA diversity are consistent with a progenitor-derivative relationship between the species, but they are inconsistent with a reduction in population size during the founding of the derivative.
For more information on ongoing projects, visit the other People in the Lab.
- a large
allopolyploid genus in the wheat tribe
Long fields of barley and of rye,
That clothe the wold and meet the sky
-Alfred Lord Tennyson, 1842. "The Lady of Shalott"
bounteous lady, thy rich leas
remember me when the west wind moves
the focus of many evolutionary studies
nurse hurried over and whispered to Renshaw, and Mitty saw the man turn
research: supported by the National
DEB-9974181 and DEB-0426194.