ABSTRACT The ability to detect and respond to environmental signals is fundamental in coordinating floral induction in plants to favourable conditions. An important flowering time cue is day length and it is proposed that light signals are perceived and measured by an interaction between photoreceptors and an internal pacemaker, the circadian clock. The control of flowering has been best characterised in the model plant Arabidopsis thaliana L. Heynh (Arabidopsis). The GIGANTEA (GI) gene has a complex role in both the promotion of flowering in response to photoperiod and the regulation of the circadian clock. The expression of GI is under circadian control and is affected by day length, light quality and temperature changes. The GI protein is also circadian regulated and is actively degraded in the dark. The biochemical function of GI is unknown and one method to elucidate the role of this protein is to identify protein interactors. The aim of this thesis project was to characterise proteins that interacted with GI. Previously, the BELL-LIKE HOMEODOMAIN 3 (BLH3) protein was identified as a putative GI protein interactor. As part of this thesis work, yeast 2-hybrid and in vitro pull down assays were utilised to confirm the interaction between GI and BLH3. Sequence and phylogenetic analyses were used to further examine the BELL family of proteins. The BELL-LIKE HOMEODOMAIN 10 (BLH10) protein was found to be closely related to BLH3 and also interacted with GI. Reverse 2-hybrid assays were used to determine the regions or domains within the GI, BLH3 and BLH10 proteins required to mediate protein interactions. Expression assays established that the BLH3 and BLH10 transcripts were present throughout plant tissues and times of development. Further analyses revealed that BLH3 and BLH10 are not directly regulated by the circadian clock. The results of GFP expression assays demonstrated that the BLH3 protein is localised to the nucleus in plant cells. Transgenic blh3 and blh10 mutant plants were identified and analysed for flowering and light response phenotypes. BLH3 and BLH10 do not function with GI in the photoperiodic pathway to control flowering, yet the blh3 and blh10 mutants do have a flowering phenotype in short day conditions. Like gi, the blh3 and blh10 mutants exhibited exaggerated hypocotyl elongation in response to red and low light conditions. These results are suggestive of a role for BLH3, BLH10 and GI in flowering and deetiolation responses to specific light conditions in plants. / This PhD research was sponsored by Dr George Mason

ABSTRACT The ability to detect and respond to environmental signals is fundamental in coordinating floral induction in plants to favourable conditions. An important flowering time cue is day length and it is proposed that light signals are perceived and measured by an interaction between photoreceptors and an internal pacemaker, the circadian clock. The control of flowering has been best characterised in the model plant Arabidopsis thaliana L. Heynh (Arabidopsis). The GIGANTEA (GI) gene has a complex role in both the promotion of flowering in response to photoperiod and the regulation of the circadian clock. The expression of GI is under circadian control and is affected by day length, light quality and temperature changes. The GI protein is also circadian regulated and is actively degraded in the dark. The biochemical function of GI is unknown and one method to elucidate the role of this protein is to identify protein interactors. The aim of this thesis project was to characterise proteins that interacted with GI. Previously, the BELL-LIKE HOMEODOMAIN 3 (BLH3) protein was identified as a putative GI protein interactor. As part of this thesis work, yeast 2-hybrid and in vitro pull down assays were utilised to confirm the interaction between GI and BLH3. Sequence and phylogenetic analyses were used to further examine the BELL family of proteins. The BELL-LIKE HOMEODOMAIN 10 (BLH10) protein was found to be closely related to BLH3 and also interacted with GI. Reverse 2-hybrid assays were used to determine the regions or domains within the GI, BLH3 and BLH10 proteins required to mediate protein interactions. Expression assays established that the BLH3 and BLH10 transcripts were present throughout plant tissues and times of development. Further analyses revealed that BLH3 and BLH10 are not directly regulated by the circadian clock. The results of GFP expression assays demonstrated that the BLH3 protein is localised to the nucleus in plant cells. Transgenic blh3 and blh10 mutant plants were identified and analysed for flowering and light response phenotypes. BLH3 and BLH10 do not function with GI in the photoperiodic pathway to control flowering, yet the blh3 and blh10 mutants do have a flowering phenotype in short day conditions. Like gi, the blh3 and blh10 mutants exhibited exaggerated hypocotyl elongation in response to red and low light conditions. These results are suggestive of a role for BLH3, BLH10 and GI in flowering and deetiolation responses to specific light conditions in plants. / This PhD research was sponsored by Dr George Mason

Thesis (M.S.)--West Virginia University, 1999. / Title from document title page. Document formatted into pages; contains ix, 80 p. : ill. (some col.) Includes abstract. Includes bibliographical references (p. 60-69).

Title from title page of PDF (University of Missouri--St. Louis, viewed March 22, 2010). Includes bibliographical references.

Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 106-117).

Thesis (Ph. D.)--Princeton University, 1987. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (v. 1, leaves 391-406).

Thesis (M.S.)--University of Wisconsin--Madison, 1965. / eContent provider-neutral record in process. Description based on print version record. Bibliography: l. 62-63.

Thesis (Ph. D.)--University of Tennessee, Knoxville, 2010. / Title from title page screen (viewed on July 13, 2010). Thesis advisor: Robert N. Trigiano. Vita. Includes bibliographical references.

Reproductive endpoints are generally not considered in regulatory risk assessments used to inform registration decisions for pesticides, and relatively few studies have examined effects of herbicides on reproduction in non-target plants. In two sets of greenhouse experiments using three wild species (Rudbeckia hirta L., Centaurea cyanus L. and Trifolium pratense L), effects on flowering phenology and inflorescence characteristics were investigated following low, drift-equivalent glyphosate exposure at an early bud stage. Weekly post-spray observations included the number of inflorescences, aborted buds and malformed inflorescences. In the experiment focusing on inflorescence characteristics (C. cyanus and T. pratense only), inflorescences and pollen were collected at five weeks post-spray to measure inflorescence dry weight, count the number of reproductive florets, estimate the amount of pollen per floret, and assess pollen germination in vitro. Flower production was adversely affected in all three species, including delays in flowering, significant increases in the number of aborted buds and malformed inflorescences, an overall reduction in the number of inflorescences produced, as well as a reduction in the duration of individual inflorescence bloom time (R. hirta and T. pratense assessed only). Inflorescence dry weight and in vitro pollen germination were significantly reduced for C. cyanus exposed to glyphosate, but not for T. pratense. However, both species experienced a significant reduction in the number of reproductive florets produced per inflorescence in response to glyphosate exposure. Neither species was observed to have significant reductions in the amount of pollen produced per reproductive floret. These results have important implications for risk assessment, demonstrating that current glyphosate use in Canada and elsewhere could be adversely affecting non-target flowering plants in field margins, as well as other taxa that rely on them, particularly pollinators. Les effets sur la reproduction des plantes ne sont généralement pas pris en ligne de compte dans les évaluations réglementaires sur les risques des pesticides lors de leur homologation. De plus, relativement peu d'études ont examiné les effets des herbicides sur la reproduction des plantes non ciblées. Dans deux séries d'expériences en serres avec trois espèces sauvages (Rudbeckia hirta L., Centaurea cyanus L. et Trifolium pratense L), les effets sur la phénologie florale et les caractéristiques des inflorescences ont été étudiés après une faible exposition au glyphosate équivalente à la dérive durant la pulvérisation lorsque les plantes sont au début des boutons floraux. Des observations hebdomadaires post-pulvérisation ont été effectuées sur le nombre d'inflorescences, de bourgeons avortés et d’inflorescences malformées. Dans l'expérience portant sur les caractéristiques des inflorescences (C. cyanus et T. pratense seulement), les inflorescences et le pollen ont été recueillis cinq semaines après la pulvérisation pour mesurer le poids sec des inflorescences, compter le nombre de fleurons reproducteurs, estimer la quantité de pollen par fleur et évaluer la germination du pollen in vitro. La production de fleurs a été affectée chez les trois espèces, y compris des retards de floraison, des augmentations significatives du nombre de bourgeons avortés et d’inflorescences malformées, une réduction globale du nombre d'inflorescences produites et une diminution de la durée de floraison par inflorescence. (R. hirta et T. pratense évalués seulement). Le poids sec des inflorescences et la germination in vitro du pollen ont été significativement réduits chez C. cyanus exposé au glyphosate, mais pas chez T. pratense. Cependant, les deux espèces ont subi une réduction significative du nombre de fleurons reproducteurs produits par inflorescence en réponse à l'exposition au glyphosate. Aucune des deux espèces n'a montré de réduction significative de la quantité de pollen produit par fleuron. Ces résultats ont des implications importantes pour l'évaluation de risques, démontrant que le glyphosate, tel qu’utilisé présentement au Canada et ailleurs, pourrait nuire aux plantes à fleurs non ciblées retrouvées en bordure de champs, ainsi qu'à d'autres taxons qui en dépendent, particulièrement les pollinisateurs.

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