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The Drosophila morgue gene was identified as a regulator of programmed cell death and protein ubiquitination. It has been shown to enhance programmed cell death via promoting the turnover of DIAP1, a conserved anti-apoptotic protein. Morgue protein contains a zinc finger motif, an F box domain and a ubiquitin E2 conjugase variant domain with a Cysteine to Glycine substitution at the catalytic site. This unique domain/motif architecture suggests that Morgue may have very distinctive activities. However, how and what each domain/motif contributes to Morgue function remains unexplored. My dissertation project focused on a study of Morgue protein evolution and function using a combination of bioinformatics, genetics and biochemical methods. The results suggest that Morgue exhibits widespread but restricted phylogenetic distribution among invertebrate metazoans; the study of Morgue's origin provides an example of how multi-domain proteins may evolve. Results of functional studies revealed that over-expression of Morgue can induce a homozygous lethal phenotype that is independent of either F-box or the Glycine in the UEV domain. In addition, co-immunoprecipitation experiments have shown that Morgue associates with SkpA and Lys48 linked polyubiquitin chains, indicating that Morgue might be a multi-functional protein in PCD and ubiquitination.

Brachypodium distachyon (brachypodium) is a temperate grass that has great promise as a model system to study grass-specific traits for crop improvement. Under iron (Fe)-deficient conditions, grasses synthesize and secrete Fe(III)-chelating agents called phytosiderophores (PS). In maize, Yellow Stripe1 (ZmYS1) is the transporter responsible for uptake of Fe(III)-PS complexes from the soil. Some members of the family of related proteins called Yellow Stripe-Like (YSL) have roles in internal Fe translocation of plants, while the function of other members remains uninvestigated. One aim of this study was to establish brachypodium as a model system to study Fe homeostasis in grasses. HDMA was detected as the dominant type of PS secreted by brachypodium, and its secretion is diurnally regulated in parallel to that of related species such as barley and wheat. Nineteen YSL family members were identified in brachypodium, and their expression profiles in response to Fe deficiency were analyzed. Phylogenetic analysis revealed that some YSLs group into a grass-specific clade, and expression of the BdYSL members of this clade could not be detected in shoots or roots, suggesting grass-specific functions in reproductive tissues. The Fe status of the plant can regulate expression of several BdYSL genes in both shoots and roots suggesting roles in Fe homeostasis. Brachypodium YS1 knockdown lines were also generated to test Fe(III)-PS transport abilities of certain YSL proteins. In the context of this dissertation, an EMS mutagenized population of brachypodium was produced. One mutant with the iron deficiency symptom interveinal chlorosis was characterized. Metal content analyses revealed that mutant plants are low in Fe, Zn and Cu. Mutant plants are capable of synthesizing PS in normal amounts, but they do not release the PS from roots into the soil solution, suggesting that gene underlying this mutation functions to allow secretion of PS. Performing bulk segregant array mapping and fine mapping using SNP markers, the location of this new mutation was mapped to a 1.7Mb interval on chromosome 5. Cloning of this gene is likely to fill in the missing part of the iron uptake mechanism in grasses.

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