Date of Award
2018
Degree Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Graduate Group
Biology
First Advisor
Scott Poethig
Abstract
As plants age, the morphology and physiology of the shoot changes—a
phenomenon known as vegetative phase change. Often these changes are
important in the life history of the plant and contribute to shifting strategies in
growth, defense, and competition. The temporally regulated microRNAs miR156
and miR157 are known to control many aspects of vegetative phase change
making them ideal for examining how this pathway contributes to the evolution of
life history strategies. In this work, I examine this question using two genera of
woody legumes.
First, I use the New World Ant-Acacias (genus Vachellia) to examine if
age-dependent changes in plant defenses evolve as a consequence of neutral
constraints on development. I find that the miR156/157 pathway likely controls
the age-dependent appearance of the swollen-thorn syndrome—a suite of traits
important for interaction with mutualistic ants. This finding is in disagreement with
the idea that the temporal regulation of the swollen-thorn syndrome has evolved
as a consequence of selectively neutral processes such as ontogenetic drift and
supports the idea that the timing of syndrome emergence is somehow adaptive. I
discuss the possible agents of this selection and their relation to the miR156/157
pathway.
I also investigate the frequency of life-history heterochrony and its
mechanism using plants of the genus Acacia, which undergo a conspicuous shift
in leaf morphology during their life cycle. This transition from a compound leaf to
a simple-horizontally expanded leaf, known as a phyllode has previously been
linked to the miR156/157 pathway. Using this morphological marker of vegetative
iiiphase change I examine the timing of this transition in 147 species within a
phylogenetic context. I find that the evolution of a prolonged or persistent juvenile
phase has evolved independently at least 7 times in Acacia. For two of these
events the rate and magnitude of miR156 decline is reduced supporting the idea
that these species are neotenous. I use genome sequencing to characterize the
MIR156/MIR157 gene families, and identify a gene with a mutation in a putative
cis-regulatory element that may contribute to phenotypic differences between
species.
Recommended Citation
Leichty, Aaron, "The Evolution Of The Mir156/157 Pathway In Woody Legumes" (2018). Publicly Accessible Penn Dissertations. 3142.
https://repository.upenn.edu/edissertations/3142
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