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 Physiological and Molecular Studies of Ethylene Effects on Soybean Root Infection by Soybean Cyst Nematodes(2007-12-10) Xue, Ping; Solomos, Theophanes; Tucker, Mark L.; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Soybean cyst nematode (SCN), Heterodera glycines, is one of the most devastating pests of soybean in the world. Several earlier reports demonstrated that ethylene is involved in nematode feeding cell formation in Arabidopsis and tomato. I investigated whether or not ethylene is involved in SCN feeding cell formation in soybean. My results show that SCN parasitism was increased by treatment of roots with ethylene and inhibited by suppressors of ethylene action or in an ethylene resistant soybean mutant. My results also indicate that excised soybean roots colonized by SCN produced ethylene at 1.5-3 times the rate of non-infected roots between 14 and 22 days post inoculation. To determine if ethylene was being synthesized in feeding cells, an ethylene-responsive promoter fused to a GUS reporter gene was constructed and transformed into soybean roots with Agrobacterium rhizogenes. Overall, the results suggest that ethylene plays an important role in SCN infection in soybeanItem Characterization and Expression of RUB1 Conjugase and Cullin1-like Genes in Poplar Associated with Vegetative Bud Development and Dormancy(2006-06-12) Saritas-Yildirim, Banu; Coleman, Gary D; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Dormancy is an adaptive trait that ensures survival of plants in adverse growth conditions. By using phylogenetical, expression, and protein analysis, RUB1 conjugase and Cullin1 were characterized in poplar dormancy. RUB1 conjugase and Cullin1 were annotated using sequence homology approach. RUB1 conjugase was expressed in apical buds during dormancy but not detected in those of etr1-1 expressing poplars. Its transcript abundance was reduced in axillary buds, leaves and bark of etr1-1 expressing poplars compared to wild types. RUB1 conjugase expression was not affected by AVG but reduced by 50µM ACC in apical buds of etr1-1 expressing poplars. Cullin1 and EBF expression did not display significant difference in most tissues except for the Cullin1 expression in middle and bottom leaves during short-day treatments in wild types. Two novel RUB1-conjugated proteins were detected during low temperature treatments. This study has built a foundation for further analysis of targeted protein degradation in dormancy.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.Item Biology of Ophiosphaerella agrostis, epidemiology of dead spot, and a molecular description of the pathogen(2004-10-21) Kaminski, John; Dernoeden, Peter H.; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Ophiosphaerella agrostis is a newly described pathogen that incites dead spot disease of creeping bentgrass (Agrostis stolonifera) putting greens throughout the eastern United States. The objectives of this research project were to: 1) monitor environmental conditions and develop a predictive model for disease progress and pathogen dispersal under field conditions; 2) determine the effect of various fertilizers on dead spot recovery in bentgrass; and 3) develop molecular methods to diagnoses the disease and determine genetic variation among O. agrostis isolates. Field studies showed that the appearance of dead spot infection centers was influenced predominantly by air (greater than or equal to 18 degrees Centigrade) and soil (greater than or equal to 20 degrees Centigrade) temperature, but other factors including low relative humidity (less than or equal to 80%), shortened periods of leaf wetness (less than or equal to 14 hours), and high levels of solar radiation (greater than or equal to 230 W m to the minus 2) were associated with the development of dead spot epidemics. Patch diameter of O. agrostis infection centers and pseudothecia production generally increased at a linear rate between mid-June and early to mid-August. In a growth chamber study, ascospores were released from pseudothecia following a sharp decrease in relative humidity. Field studies revealed that ascospore release occurred primarily at dawn and dusk or during precipitation events. During precipitation events, ascospores may be forcefully discharged during the entire event, but most ascospores are released within the first 10 hours after precipitation begins. O. agrostis successfully over-wintered in bentgrass leaf sheaths, crowns, roots, and stolons, but little or no reactivation of the disease occurred in the second year. Plots treated with ammonium sulfate and isobutylidene diurea were among the fastest and slowest to recover from dead spot, respectively. In the second year (2003), dead spot recurred in plots treated since 2002 with KNO3, Ca(NO3)2, urea, and a complete fertilizer (20-20-20), but disease symptoms did not recur in plots receiving ammonium sulfate. Species-specific primers capable of detecting O. agrostis at very low concentrations (5 pg DNA) were developed and can be used to assist in diagnosing dead spot. Amplified fragment length polymorphism (AFLP) DNA fingerprinting resulted in placement of isolates (n=77) into three distinct clades that were greater than or equal to 69% similar.