There is room available for undergraduate students to work in my laboratory. Please email Dr. Howarth.
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.
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 – 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.
Howarth, D. G. and M. J. Donoghue. Duplications and expression of DIVARICATA-like genes in Dipsacales. Mol. Biol. and Evol. submitted Aug 2008.
Howarth, D. G. and M. J. Donoghue. 2006. Phylogenetic Analysis of the “ECE” (CYC/TB1) Clade Reveals Duplications Predating the Core Eudicots. Proc. Nat. Acad. Sci. USA 103(24): 9101-9106.
Howarth, D. G. and M. J. Donoghue. 2005. Duplications in CYC-like genes from Dipsacales correlate with floral form. Int. J. Plant Sci. 166(3): 357-370.
Howarth, D. G. and D. A. Baum. 2005. Genealogical evidence of homoploid hybrid speciation in an adaptive radiation of Scaevola (Goodeniaceae) in the Hawaiian Islands. Evolution 59(5): 948-961.
Randell, R. A., D. G. Howarth, and C. W. Morden. 2004. Genetic analysis of natural hybrids between endemic and alien Rubus (Rosaceae) species in Hawai’i. Conservation Genetics 5: 217-230.
Howarth, D. G., M. H. G. Gustafsson, D. A. Baum, and T. J. Motley. 2003. Phylogenetics of the genus Scaevola (Goodeniaceae): Implications for dispersal patterns across the Pacific Basin and colonization of the Hawaiian Islands. American Journal of Botany 90(6): 915-923.
Howarth, D. G., and D. A. Baum. 2002. Phylogenetic Utility of a Nuclear Intron from Nitrate Reductase for the study of closely related plant species. Molecular Phylogenetics and Evolution. 23: 525-528.
Howarth, D. G., D. Gardner, and C. Morden. 1997. Evolution and Biogeography of Rubus Subgenus Idaeobatus (Rosaceae) in the Hawaiian Islands. Syst. Bot. 22(3): 433-441.
Howarth, D. G. and M. J. Donoghue. Phylogeny and expression of TCP and MYB genes and their role in floral symmetry shifts in core eudicots and Dipsacales. Botany Meetings 2008.
Howarth, D. G. The Attraction of Flowers: Stories of their Evolution, Genes and Development. St John’s University Seminar, Feb. 2008.
Howarth, D. G. and M. J. Donoghue. Phylogeny and expression of TCP and MYB genes and their role in floral symmetry shifts in Dipsacales, Botany Meetings 2007.
Howarth, D. G. and M. J. Donoghue. Phylogeny and expression of TCP and MYB genes and their role in floral symmetry shifts in Dipsacales. New York Area Plant Molecular Biology Meeting, Yale University, June 2007.
Howarth, D. G. and M. J. Donoghue. Evolution of floral symmetry genes (including CYCLOIDEA): Gene duplications and diversifying expression. Evolution Meetings 2006.
Howarth, D. G. and M. J. Donoghue. Sequences from Dipsacales suggest deep eudicot duplications in the floral symmetry TCP genes. Botany Meetings 2004
Howarth, D. G. and M. J. Donoghue. Sequences from Dipsacales suggest deep eudicot duplications in the floral symmetry TCP genes. Evolution Meetings 2004.
Howarth, D. G. and D. A. Baum. Genealogical evidence of homoploid hybrid speciation in an adaptive radiation of Scaevola (Goodeniaceae) in the Hawaiian Islands. Evolution Meetings 2004.
Howarth, D. G. Evolution of Scaevola (Goodeniaceae), Bernice P. Bishop Museum special seminar, Hawaii. 2003.
Howarth, D. G., and D. A. Baum. Comparing three variable nuclear intron regions and nrDNA ITS to determine the phylogenetic history and a possible hybrid origin in a closely related Hawaiian clade in Scaevola (Goodeniaceae). Botany 2002 (Abstract).
Howarth, D. G. 2002. Evolution on Islands: Dispersal, Speciation, and Hybridization in Scaevola (Goodeniaceae) in the Hawaiian Archipelago. Department of Ecology and Evolutionary Biology special seminar, Yale University.
Howarth, D. G., T. J. Motley, and M. H. G. Gustafsson. 1999. Phylogenetics and Biogeography of Scaevola in the Pacific Basin. International Botanical Congress XVI (Abstract).