Plant Science & Landscape Architecture Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2797
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Item TYPE II MADS-BOX GENES ASSOCIATED WITH POPLAR APICAL BUD DEVELOPMENT AND DORMANCY(2008-04-25) Chen, Kuang-Yu; Coleman, Gary D; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)MADS-box transcription factors regulate the development of vegetative and reproductive organs in plants. Little is known about the role of MADS-box genes in tree development. Using phylogenetic analysis, 57 putative type II MADS-box genes representing 14 functional classes were identified in the Populus trichocarpa genome. cDNA sequencing of the poplar type II MADS-box genes indicates that 28.1% of the transcripts differed in the intron-exon structures predicted in the genome database and 19.3% of the transcripts appear to be alternatively spliced. The majority of the poplar type II MADS-box genes were expressed in a wide variety of tissues including shoot apices, leaves, bark, xylem, root, and floral tissues and in shoot apices during bud development and dormancy. These results indicate that poplar MADS-box genes have diverse regulatory roles in a broad range of tissues and developmental processes. Six poplar FLC-like genes, PtFLC1-PtFLC6, were identified in the poplar genome and expression of all six genes was detected in poplar shoot apices. The expression of one gene, PtFLC2, declined in apical buds during SD photoperiod and low temperature induced dormancy development suggesting a role in bud dormancy and may represent an analogous regulatory mechanism to the down-regulation of FLC during vernalization in Arabidopsis. In addition, several PtFLC2 splice isoforms (PtFLC2as1-9) were identified that were associated with the later stages of bud dormancy. Overexpression of the PtFLC2as1 isoform delayed photoperiod induced apical bud development and bud dormancy, growth cessation, and leaf senescence while overexpression of the PtFLC2as2 isoform appeared to accelerate bud development and dormancy and reduce the amount of chilling required to overcome dormancy. These findings suggest that PtFLC2, unlike Arabidopsis FLC, could be an integration point for both photoperiod and cold signals that regulate bud development and dormancy. These results also suggest that in addition to transcriptional regulation, that cold-mediated production of PtFLC2 splicing isoforms may have an important regulatory role in bud dormancy. The regulated production of splicing isoforms could regulate bud dormancy either by dominate negative interactions, by forming different protein complexes or regulating different pathways that regulate growth, dormancy, and dormancy release.Item The effects of solar ultraviolet-b on the proteome and antioxidant defense systems in soybean leaves(2007-04-24) Xu, Chenping; Sullivan, Joe H.; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Stratospheric ozone depletion has caused an increase in the amount of ultraviolet-B (UV-B) radiation reaching the earth's surface. Some investigations have demonstrated that UV-B has effects on protein accumulation and active oxygen species (AOS) metabolism in plants. Because of the unrealistically high UV-B level and low levels of ultraviolet-A (UV-A) and photosythetically active radiation (PAR) in indoor studies it has been questioned whether results from these studies can be extrapolated to field responses. In the present study two isolines of the soybean cultivar Clark with different flavonoid contents were grown in the field with or without natural levels of UV-B. The leaf proteome and AOS metabolism were examined. Ambient solar UV-B radiation changed AOS metabolism by decreasing superoxide dismutase activity and increasing the activities of ascorbate peroxidase, catalase and glutathione reductase relative to UV-B exclusion treatments. This resulted in decreased ascorbic acid and increased dehydroascorbate content. Proteomic analysis showed that the accumulations of 67 protein spots were significantly affected by solar UV-B. Proteins related to photosystems in photosynthesis were increased in abundance while enzymes involved in the primary carbon and nitrogen metabolism were decreased. This could lead to overreduction of the photosynthetic electron transport chain and enhance the formation of superoxide radicals and singlet oxygen. The magenta line, which has reduced flavonoid levels, had greater proteomic and oxidative responses than the standard line, suggesting that flavonoids act as screening compounds and antioxidants in protecting plants from UV-B radiation. These line-specific differences occurred even under UV-B exclusion, which may be due to high UV-A, PAR or temperature. More detailed studies are needed to elucidate the effects of other environmental factors on the soybean leaf proteome and AOS metabolism under field conditions.Item TRANSCRIPT PROFILING AS A METHOD TO STUDY FRUIT MATURATION, TREE-RIPENING, AND THE ROLE OF "TREE FACTOR" IN 'GALA' AND 'FUJI' APPLES(2005-04-20) Lin, Shu-fei; Walsh, Christopher S; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)'Gala' and 'Fuji' are two high-quality apple (Malus domestica Borkh) cultivars. Their fruits mature and tree-ripen over a long period of time, and are resistant to pre-harvest drop. "Tree factor," a putative inhibitor of system 2 ethylene production is hypothesized to account for differences in ethylene production between attached and detached apple fruits. Three years of field data revealed two distinct patterns of maturation and ripening behavior in these two cultivars. 'Gala,' an early cultivar, demonstrated a typical positive "tree factor." Studies of the ripening pattern of 'Fuji' apple, which is a late-maturing cultivar, did not. 'Fuji' data were confounded by cold weather in the late fall. The natural progression of tree-ripening did not lead to the high concentrations of internal ethylene routinely measured in stored fruits. The stimulation of ethylene found in picked 'Gala' fruits ripened in the orchard might be explained by wounding stress coupled with a loss of nutrients and the water stress. Our alternative explanation for "tree factor" is the effect of continued termination of the phloem and xylem connection. The strength of the "tree factor" declined as 'Gala' fruit maturity progressed. Therefore, the "tree factor" tends to be more obvious in fruits with shorter growing period that mature during warm weather. To investigate differential gene expression that accompanies maturation and tree ripening, we used cDNA-AFLP (Amplified Fragment Length Polymorphism) to identify changes in transcript profiling during tree-ripening, and in the ripening of harvested fruits. Two hundred differentially-expressed transcript-derived fragments were isolated from 'Gala.' Ripening-related genes including those known to function in the key processes of defense and stress, cell wall degradation, pigment production and aroma biosynthesis were identified. Clones similar to housekeeping genes involved in protein biosynthesis and degradation, intracellular trafficking and sorting, cell structure and mobility, and metabolism-associated genes were also isolated. Expression patterns of these transcript-derived fragments were verified by using a different 'Gala' sample set on microarray and/or Northern blots. Our study supports the hypothesis that many ripening processes are under transcriptional control and that most of these differentially-expressed genes are highly conserved in fruits.