Thesis (Ph. D.)--Rutgers University, 2007. / "Graduate Program in Plant Biology." Includes bibliographical references.

Thesis (Ph. D.)--Rutgers University, 2007. / "Graduate Program in Plant Biology." Includes bibliographical references (p. 191-229).

Thesis (M.S.)--Rutgers University, 2008. / "Graduate Program in Plant Biology." Includes bibliographical references (p. 42-46).

Thesis (Ph. D.)--Rutgers University, 2008. / "Graduate Program in Plant Biology." Includes bibliographical references (p. 210-225).

No description available.

No description available.

Aquaporins (AQPs) are channel proteins that facilitate the transport of water and various low molecular weight solutes including metalloids. Plant aquaporins have been divided into four major subfamilies: plasma membrane intrinsic proteins (PIPs), NOD26-like intrinsic proteins (NIPs), tonoplast intrinsic proteins (TIPs), and small basic intrinsic proteins (SIPs). Various studies have shown that the transport of metalloids including arsenite, antimonite, silicon and boron in plants is facilitated by members of NIP subfamily. In this study, we provided experimental evidences showing that members of rice PIP subfamily are involved in arsenite and boron permeability. RT-PCR analysis of seven OsPIPs; OsPIP1;2, OsPIP1;3, OsPIP2;4, OsPIP2;5, OsPIP2;6, OsPIP2;7, and OsPIP2;8 showed that these genes were downregulated under arsenite toxicity in shoots and roots. Whereas, these OsPIP genes were deferentially regulated in shoots and highly induced in roots by boron toxicity. Heterologous expression in Xenopus laevis oocytes showed that OsPIP2;4, OsPIP2;6, and OsPIP2;7 significantly increased the transport of arsenite. Expression of OsPIP candidate genes in HD9 yeast strain lacking the metalloids influx and efflux systems resulted in an increased boron sensitivity and accumulation. Overexpression of two OsPIP candidates; OsPIP1;3 and OsPIP2;6 in Arabidopsis yielded enhanced arsenite and boron tolerance with higher biomass and greater root length compared to wild type plants, however there was no difference in arsenic and boron accumulation in long-term uptake assays. Short duration exposure to AsIII resulted in both active influx and efflux of As in shoots and roots, suggesting a bidirectional transport activity of OsPIPs. Whereas, short-term uptake assay of tracer B (10B) in shoots and roots demonstrated increased 10 B influx in transgenic Arabidopsis lines indicating that these OsPIPs are also involved in mediating B transport in plants. We used RNAi approach to knockdown the expression of OsPIP1;3 and OsPIP2;6 in rice. We generated RNAi lines for both genes and qRT-PCR analysis showed a significant decrease in the transcript levels for OsPIP1;3 and OsPIP2;6. These RNAi lines will be the subject of future studies. These OsPIPs genes will be highly useful in developing arsenite and boron tolerant crops for enhanced yield in the areas affected by high As and B toxicity.

The prevalence of allergic disease is expected to increase with climate change. Grasses, which have highly allergenic pollen, are widely distributed across the globe. Changes in production and allergen content of grass pollen have not been specifically investigated. We tested the effects of elevated carbon dioxide and ozone on growth, pollen and allergen production of Timothy grass (Phleum pratense L.). Timothy is also used as an agricultural forage crop so changes in plant productivity can also affect humans indirectly. Plants were fumigated in eight chambers at two concentrations of ozone (O 3; 30 and 80 ppb) and carbon dioxide (CO2; 400 and 800 ppm) to simulate present and future projected levels. Destructive harvests were completed every three weeks to measure productivity. Pollen was collected in polyethylene bags placed around flowers and assessed for pollen number and concentration of the allergenic protein, Phl p 5. We found that elevated CO2 significantly increased the amount of pollen produced per flower regardless of O3 level. In addition, the amount of Phl p 5 allergen per flower was significantly increased in plants grown at elevated CO 2 / low O3 conditions. We also found that plants grown in both elevated CO2 and elevated O3 increased the amount of pollen produced per weight of flower. The Phl p 5 allergen content per pollen grain was significantly reduced by elevated O3, as was flower length and weight. However, this was partially ameliorated by elevated CO 2. Productivity was affected negatively by elevated O3 throughout the life cycle. CO2 increased shoot productivity during the intermediate stages of life and also ameliorated the negative impacts of elevated O 3. We conclude that increasing levels of CO2 will cause a 2.5 times increase in Timothy grass pollen production thus increasing human airborne pollen exposure. Increases in pollen were likely a result of increased shoot biomass in the stages leading up to reproduction. If Timothy grass is a good model for other grasses, this portends for increased allergy suffering worldwide and an important health impact of global climate change.

Trees exhibit many unique aspects of plant biology, one of which is the formation of wood. Wood is one of the most important natural products with a multitude of applications. The formation of wood (xylogenesis) is a highly ordered developmental process involving the patterned division and differentiation of the vascular cambium into secondary xylem and phloem tissue types. The progression of xylogenesis developmental process requires differential gene expression across the different tissue types. The tight regulation of wood formation is mediated by genes that regulate cambial meristem differentiation and xylem cell fate. MicroRNAs (miRNAs) are a group of endogenous ~ 20 to 24 nt RNA molecules that down regulate gene expression at the post-transcriptional level. MicroRNAs have validated roles in developmental processes through the regulation of meristem cell differentiation and developmental patterning in plants. They have been shown to spatially regulate differential gene expression patterns at different developmental stages. Thus, the vascular cambium and its derivatives are excellent candidate tissues for miRNA discovery. The aim of this M.Sc. study was to isolate microRNAs from actively differentiating tissues of two tree species in order to determine possible gene regulatory networks involved in early meristem differentiation, tissue patterning and secondary vascular development. A small RNA library from two-month old in vitro Populus trichocarpa plantlets was constructed to identify putative miRNAs contributing to the early postembryonic development of trees. This library, in conjunction with computational prediction of poplar miRNA homologues and precursor secondary structures, was used to identify a total of 72 poplar miRNAs. Sixteen of these were putative novel miRNAs, belonging to nine new miRNA families. A genome-wide search identified 55 putative target genes for the newly identified miRNAs. The target genes had diverse biological roles in developmental events and maintenance of cellular homeostasis. A number of the predicted targets were involved in plant organ development such as leaf cell fate, floral organ development and meristem differentiation. Other targets were involved in response to hormones, such as growth regulating factors and signaling proteins. Additionally, several targets were related to cellular metabolic processes, such as protein modification and ubiquitination. By isolating miRNAs from developing poplar plantlets, we were able to suggest possible developmental programmes under the control of these molecules, possibly affecting early seedling development and growth. A similar approach was used to identify miRNAs from three differentiating vascular tissues of Eucalyptus grandis. Isolated small RNA sequences were used in a search against all available bacterial artificial chromosome (BAC) shotgun genomic sequences from an ongoing Eucalyptus camaldulensis genome sequencing initiative at the Kazusa DNA Research Institute in Japan. We were able to characterize the first Eucalyptus miRNAs, and identified 48 putative miRNAs grouping into thirteen gene families. Twenty of the miRNAs belong to five families previously identified in other plant species, whereas the remaining 28 miRNAs grouped into eight putative novel miRNA families. Searches of the Populus and Arabidopsis annotated genomes revealed 45 putative target genes for the new families. Targets of particular interest included transcription factors involved in cell fate determination, including a MADS-box transcription factor involved in xylem formation. Further targets included auxin signaling proteins and auxin response factors, which could play a significant role during auxin regulation of vascular development. Expression profiling of the putative miRNAs using quantitative RT-PCR revealed that a number of the miRNAs exhibited differential expression patterns across xylogenic and non-xylogenic tissues. One miRNA showed expression in a single vascular tissue, whereas others were expressed at varying levels across the vascular tissues. This observation indicates a possible role for these putative miRNAs during vascular development and differentiation in eucalypt trees. In this study we used a combination of small RNA library construction and computational prediction to identify microRNAs from two tree species. We identified a total of 120 putative miRNAs grouping into 31 families. Of these, 44 group into 17 putative novel tree-specific miRNAs. This study has allowed the identification of novel miRNAs from a unique set of tissues, and has contributed to the ever-growing number of plant-specific miRNAs. The results of this study further contribute to our expanding knowledge of the unique developmental process of vascular tissue differentiation of perennial woody plants such as Eucalyptus and Populus species. / Dissertation (MSc (Genetics))--University of Pretoria, 2006. / Genetics / unrestricted

No description available.