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Howarth Lab Research

Areas of Specialization:

Evolution of Development

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.

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