Vegetative Phase Change in Arabidopsis                            

Plant shoots undergo major changes in their morphology and physiology at several different times in their development  We are interested in the transition from the juvenile to the adult phase of vegetative development, which is known as vegetative phase change.  Genetic and molecular  analyses of vegetative phase change in annual and perennial plants have revealed that it is regulated by the related miRNAs, miR156 and miR157, which act by repressing members of the SPL family of transcription factors.  Vegetative phase change occurs when the level of miR156/157 decreases below a certain threshold, leading to an increase in the expression of SPL genes. SPL transcription factors promote the expression of a variety of species-specific adult vegetative traits, and also contribute to an increase in reproductive competence.   We are interested in the factors responsible for the temporal expression pattern of miR156/157 in Arabidopsis thaliana, and the mechanism by which these miRNAs regulate SPL gene expression. 

The Evolution of Vegetative Phase Change in the Acacieae 

The Acacieae is a tribe of nitrogen-fixing trees and shrubs that is widespread in tropical and sub-tropical regions the the world. This tribe is of particular interest for research on the evolution and functional significance of vegetative phase change because the oldest genera in the Acacieae produce only bipinnately compound leaves, whereas species in the more recently evolved genus, Acacia, initially produce compound leaves, but then begin to produce a simple, isobilateral leaf, known as a phyllode.  Nested within the over 1,000 species of Acacia is a clade of approximately 70 species that produce only compound leaves. We are interested in the moecular mechanism of phyllode morphogenesis and the genetic basis for variation in the timing of phyllode production within this group.

New Tools for Genetic Analysis in Arabidopsis

Arabidopsis thaliana has had a major impact on plant biology over the last 20 years because of the advantages it offers for genetic analysis. The ease of performing large-scale phenotype-based genetic screens, the availability of sequence-indexed mutations in most genes, and techniques for site-specific mutagenesis and gene silencing, have all contributed to the popularity of Arabidopsis as a model system in plant biology. But, while there are many ways to obtain mutations in genes of interest in Arabidopsis, there are surprisingly few ways to efficiently manipulate mutations in genetic crosses. We are developing fluorescently-tagged transgenic lines (Traffic Lines) that allow investigators to unambiguously identify seeds homozygous or heterozygous for any mutation prior to planting. Traffic Lines also make it possible to select for recombination within a defined region of the genome. This ability enables investigators to effeciently remove linked, second-site mutations from a gene of interest, and greatly reduces the amount of molecular genotyping required for the production of near-isogenic lines.