My research integrates phylogenetic, molecular evolution,
and
developmental genetic approaches to understand evolutionary mechanisms
underlying plant development. I compare changes in the number,
sequence, expression, or function of genes across different plant groups
and determine how these changes shaped the morphology and evolution of
the groups. Currently, I am specifically studying the evolutionary
relationships of CYCLOIDEA, a TCP transcription factor involved
in
floral symmetry. In the case of TCP genes, there were three major
duplications in the CYCLOIDEA gene family that correlate with the
explosion of diverse but florally constrained eudicots (included about
70% of flowering plant species). Additionally, there were two separate
duplication events of CYCLOIDEA, which correlate with a shift
from
radially symmetric to bilaterally symmetric flowers within the group
Dipsacales.
Duplication and diversification of expression in Dipsacales CYC2
genes (From Howarth, et. al., 2011)
Additionally, I examine changes in the expression of
morphologically
important genes. For instance, CYCLOIDEA is expressed in the
upper
petals of all currently examined bilaterally symmetric flowers. There
is a different pattern in a group I study, however, Lonicera
(honeysuckle), which has a flower with four upper petals and one lower
petal vs. the more common two upper petals and three lower ones. This
morphology shift is correlated with a shift in expression, with one copy
of CYCLOIDEA found in the typical position in only the upper two
petals
and the other copy in all four of the upper petals. I also plan to
compare the function and interaction of these genes and proteins. The
newest techniques include infecting plants with a virus that knocks-down
the expressed RNA from a gene. This would allow me to examine the
change in morphology when a certain gene or gene family is effectively
turned off.
My research ultimately aims to study how the interplay of
the TCP genes
and their interacting patterns sets the developmental pattern that
determines the morphology of a flower.
Hawaiian Biogeography and Evolution
Relationships of
the endemic Hawaiian Scaevola species. Homoploid hybrid
speciation resulted in two species. (From Howarth and Baum, 2005)
My lab is also interested in the mechanisms of adaptive
radiations in
the Hawaiian Islands. Hawaiian Scaevola provides a model clade
to study the genes involved in adaptive
radiations. This is one of the few adaptive radiations in plants with a
completely resolved phylogeny, reciprocally monophyletic species, and
phenotypically diverse morphologies. A limited amount of background
molecular variation (common in plants), suggests that this clade
radiated through changes in just a few genes. Candidate genes are now
available for many of the morphological changes in Scaevola,
allowing
us
to compare both sister species pairs and hybrid species pairs to
determine discrete genes that could have played a role in the radiation
of this group. For instance, Hawaiian Scaevola flower color
varies
from
white, yellow, brown, and purple, covering different amounts of the
petals in each species. The ROSEA pathway, including a group of MYB
genes, controls anthocyanin production and is one of the better worked
out pathways in plants. Changes in this pathway could certainly affect
these flower colors. Scaevola also differs in inflorescence
architecture
(i.e., number of flowers), which LEAFY has been shown to affect in
Arabidopsis. Therefore, studying genes such as ROSEA and LEAFY
and
their
networks in Scaevola could provide insight into how and why
certain
genes change, allowing a template for adaptive radiations.