The objectives of the proposal are to provide a monographic and phylogenetic treatment of all genera and constituent species in the tribe Robinieae that are restricted to North America. I amproposing that this tribe of legumes is a model group for assessing the origins and relationships of tropical North America.
Lavin, M. 1993. Systematics of the genus Poitea (Leguminosae): inferences from morphological and molecular data. Systematic Botany Monographs 37. 87 pp. (in press).
Lavin, M., and M. Luckow. 1993. Origins and relationships of tropical North America in the context of the boreotropics hypothesis. American Journal of Botany 80(01): in press.
P.I. Mitchell-Olds, T. Mitchell-Olds, T. and D. Bradley. "Molecular, Biochemical, and Quantitative Genetics of Glucosinolates and Myrosinase in Brassica." NSF Grant No. BSR-9021451, $206,000, 1991-1993.
Dorn, L. and T. Mitchell-Olds. "Molecular and Quantitative Genetics of Flowering Time in Arabidopsis." NSF Dissertation Improvement Grant No. BSR-9016146, $10,000, 1991-1993.
Waller, D. M. and T. Mitchell-Olds. "Mechanisms of Outcrossing Advantage in Impatiens capensis." NSF Grant No. BSR 84-21272, $82,820, 1985-1987.
Coevolution of plants with insects and pathogens is influenced by allocation of the host plant's resources to defensive mechanisms or to other components of fitness. Deleterious consequences of insect or pathogen attack are well known, but possible "costs of resistance" have rarely been documented. We found resistance to one fungal pathogen caused a 14% reduction in growth rate, while resistance to a second pathogen incurred no constitutive cost to resistance. We are examining the molecular basis of plant defense through the glucosinolate-myrosinase system, a defensive pathway affecting insect and pathogen attack. In collaboration with Dr. Douglas Bradley, we have sequenced fourmyrosinase loci from Arabidopsis and Brassica, and we are developing locus-specific PCR primers to study the effects of molecular variation on individual plant fitness.
As a first step towards understanding the genetic bases of heterosis and of speciation, we are mapping genes responsible for inbreeding depression and hybrid breakdown. We have employed segregation data from our laboratory and Drs. Myerowitz and Goodman to map viability and quantitative trait loci causing inbreeding depression and hybrid breakdown in five Arabidopsis F2 populations. We have found chromosome regions with overdominant, underdominant, and epistatic effects on fitness, which may correspond to loci causing inbreeding depression or hybrid breakdown. We studied one- and two-locus segregation patterns in F2 populations ("crosses") of Arabidopsis thaliana. Overdominant viability selection was detected at two locations in one cross. Two putative overdominant loci displayed about 30% heterozygote advantage compared to neutral expectation. Thus, overdominance may contribute to inbreeding depression and heterosis in this highly self-pollinating species. Genes contributing to hybrid breakdown were also detected. Both underdominant and epistatic loci have been mapped. In several crosses, two-locus epistatic interactions favored parental genotype combinations, and viability was reduced when coadapted genotype combinations were disrupted.
Thus, we have identified chromosome regions contributing to
inbreeding depression and hybrid breakdown. Publications
resulting from funding (last 4 years only):
The objectives of this grant are to isolate and characterize the genes that encode the Arabidopsis phytochromes, analyze their patterns of expression, and develop methods to determine their individual functions. It has been shown that the phytochrome apoproteins in Arabidopsis are encoded by a family of five genes (phyA, B, C, D, and E) and these genes have been cloned and sequenced. The five phytochrome apoproteins are related in overall structure but are highly variable in their amino acid sequence, suggesting that the phy gene family arose by duplication of a precursor gene early in plant evolution. Consistent with this, degenerate primer PCR has been used to identify phy gene families similar to the Arabidopsis family in a wide range of plant species. The five phy genes are expressed at the level of mRNA and three of the phytochrome proteins have been identified in Arabidopsis plant extracts via Western blotting with type-specific monoclonal antibodies. A function for one of the five phytochromes in control of seedling growth has been assigned by analysis of photomorphogenic mutants and experiments are currently underway to complement this mutation in transgenic plants.