Page 201 - PC2019 Program & Proceedings

PLANT CANADA 2019

S187. Rapid radiation and complex genome size evolution in a clade of holocentric sedges
*1
2
4
Elliott, T. ; P. Bures ; S. Joly ; A. Muasya
3
1 Institut de recherche en biologie végétale
2 Masaryk University
4
3 Institut de recherche en biologie végétale, Université de Montréal; Department of Biological Sciences
Genome sizes across land plants exhibit huge variation, with genome expansion events occurring
predominately through polyploidy and the accumulation of repetitive DNA sequences. Another important
factor determining evolution of genome size in plants is whether a species has monocentric or holocentric
chromosomes. Whereas most plant species have monocentric chromosomes in which acentric fragments
can be lost, holocentric species have chromosomal fragments that are regularly inherited. To date,
holocentric chromosomes have only been reported in a few plant lineages, including the Cyperaceae
family (sedges). Here, we examine genome size evolution in the southern African clade of Schoenus, a
group of recently radiating sedges that are predominately restricted to nutrient-poor sandstone habitats in
the temperate areas of the southern hemisphere. We will present the results of recent phylogenetic
analyses based on paired-end genotyping-by-sequencing (GBS) data, which has been used to resolve
species relationships in other plant radiations. Our results show that genomes within Schoenus are
substantially larger than those of other closely-related groups, suggesting that polyploidy and the possible
accumulation of repetitive sequences are important mechanisms in this genus. In addition, our results
show complex clade-dependent patterns of phylogenetic resolution and genome size evolution, which
suggests rapid radiation and probable allopolyploidy. Ongoing work is focusing on improving the
sampling in this clade and further examining other aspects of genome size evolution in this lineage.

Tammy Elliott (tammy.elliott@mail.mcgill.ca)

S188. Diversity and evolution of seeds in Cuscuta (dodders, Convolvulaceae): morphology and
structure
Olszewski, M. ; M. Costea; H.A.E. Miari
*
Wilfrid Laurier University

Cuscuta is a genus of nearly 200 obligate stem parasites with subcosmopolitan distribution and
considerable agricultural and ecological significance. Dodder seeds are considered unspecialized, with no
morphological adaptations towards particular dispersal vectors; however, the seed coat anatomy has
recently suggested structural features that enable endozoochory. This is the first attempt to provide a
genus-wide overview of the diversity in morphology and anatomy of Cuscuta, together with an
assessment of the water gap and exploration of functional relationships. Subsequently, 140 species
belonging to all the four Cuscuta subgenera were surveyed. Species of the first infrageneric dodder
lineage diverged, subg. Monogynella, retain epidermal cells that are elongated and puzzle-like,
morphologically uninfluenced by dryness/wetness and an incomplete outer palisade layer. In contrast,
seeds of the other subgenera, Cuscuta, Pachystigma and Grammica, are more or less isodiametric and
have evolved the ability to alternate their morphology and physiology between two states: with deeply
pitted epidermal surface when dry, and papillose through hydration. Majority of taxa of the three subg.
excluding Monogynella have a complete outer palisade layer throughout the entirety of the seed. An
embryo with a globose radicular end has evolved in sect. Denticulatae and sect. Subulatae, likely with a
storage function. The water gap in numerous species was investigated and two mechanisms for initial
dormancy break were described. Furthermore, functional relationships between seed characters were
analyzed.

Magdalena Olszewski (olsz9360@mylaurier.ca)

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