Inflorescence diversity in the millet grasses (Paniceae, Poaceae)

I am presently working on a number of inter-related projects linking evolution and development in grasses. The first project concerns inflorescence diversity in the 'bristle clade' millet grasses. This group includes the three large genera Setaria, Pennisetum and Cenchrus, and contains foxtail millet (S. italica) and pearl millet (P. glaucum). All members of the group have bristles (sterile branchlets) as well as spikelets in the inflorescence, but inflorescences range from condensed heads with many orders of branching to elongate racemose panicles with few orders of branching. The inflorescence diversity in these three genera has been studied in a phylogenetic context, using the chloroplast markers ndhF and trnL, and has confirmed the close relationship between Pennisetum and Cenchrus, but has surprisingly suggested that both Pennisetum and Setaria are paraphyletic. The developmental analyses have shown that only a few developmental changes are need to create the diversity of inflorescences seen at maturity. Work is also underway in the lab by undergraduates Anya Penley and Shelby Kleweis, who are sequencing the nuclear markers phytochrome B and a variable intron of knotted1 respectively. These will be used to further elucidate the relationships of the subclades within the 'bristle clade', as well as to test for suspected patterns of hybridization within the group. Two papers from this work have recently been published.

A related project in the lab is a survey of inflorescence development and morphology in the panicoid grasses, a large group of some 3000 species that contains maize, sorghum and sugarcane. The survey, undertaken together with recent master's graduate Ken Hiser, master's candidate Emilie Bess and Professor Elizabeth Kellogg, is a continuation of work started by Professor Kellogg and Lucia LeRoux. A comparison of groups based on inflorescence types with groups obtained from analysis of molecular marker sequences shows that similar inflorescence forms have evolved repeatedly in different groups. This may imply that only a few genes control the developmental inflorescence morphology.

Quantitative Trait Loci (QTL) studies in foxtail millet

To examine the hypothesis that changes in inflorescence morphology are due to the action of only a few genes of largeeffect, we are doing a QTL analysis of a cross between foxtail millet (S. italica) and green millet (S. viridis), the wild species from which S. italica was domesticated. The seed for this cross was donated by our collaborators Drs. Katrien Devos and Mike Gale, of the John Innes Center, Norwich, U.K. The two parents have very different inflorescences, and the 120 segregating F2 populations show different combinations of inflorescence morphology traits. By relating the distribution of morphological traits across the F2 populations to a genomic map prepared from RFLP markers by our collaborators at the John Innes Center, we can establish areas on the chromosomes that control the expression of these traits. This work has shown that only a few major gene clusters control most of the variation in inflorescence form. Comparative mapping of QTL from the foxtail millet genome to the maize and rice genomes has allowed likely candidate genes to be identified. In several cases, map hybridization of probes of those candidate genes has shown that they are in the genome regions predicted through comparative mapping. Some QTL regions, however, do not have any likely candidate genes (as identified through similar mutant phenotypes), and these are the focus of our present investigations.

Floral development and variation in Winteraceae

My interests arising from my PhD research on floral development and floral variation in the basal angiosperm family Winteraceae are both evolutionary and structural. In particular, the method by which different floral morphologies in the family arise through modifications of the developmental process remains an important focus, especially in the Australian genus Tasmannia, where two sharply different developmental programs can be found. The study of floral variation in Drimys winteri has revealed that apical meristem size and shape have a major influence on eventual floral form. Variation in these physical parameters is dependent on the position of the flower in the inflorescence, resulting in flowers on a single tree that vary greatly in organ number and arrangement. Two papers from this work have recently been published.