Browsing by Subject "Arabidopsis thaliana"

Now showing 1 - 6 of 6
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    The Adaptive Value and Genetic Basis of Maternal Effects in Competitive Environments
    (2008-10) Dechaine Berkas, Jennifer M.
    Plants rely heavily on environmental cues to direct life-history processes. In many species, the maternal environment is a reliable predictor of environmental conditions in the next generation, and several aspects of progeny phenotype are responsive to environmental cues during seed maturation. The ratio of red to far-red light (R:FR) is one environmental cue that has been widely shown to influence plant phenotypes across generations. Low R:FR are predictive of competitive conditions, because chlorophyll in neighboring leaves absorbs red light but allows far-red light to pass through. It has been suggested that effects of the maternal competitive environment on progeny phenotype are adaptive, but very few studies have convincingly tested this hypothesis. In addition, the genetic basis of environmental maternal effects is poorly understood. In this dissertation, I examine the adaptive value and genetic basis of maternal effects in competitive environments in the plant species Brassica rapa and Arabidopsis thaliana. In chapter 1, I investigate the adaptive value of maternal effects across two generations of competitive environments in B. rapa. Maternal environment effects did not enhance progeny fitness but did influence several other progeny traits, as well as selection gradients in the progeny generation. These results suggest that although environmental maternal effects are not adaptive in this study, they are genetically variable and may evolve or affect the evolution of progeny traits. I further investigate the effects of competition on B. rapa fitness traits in chapter 2, in which I use a quantitative trait loci (QTL) mapping approach to examine how the genetic architecture of multiple components of fitness differs across competitive environments. QTL expression varied across competitive treatments for total fruit production, but QTL were generally conserved in other fitness traits. In addition, I identify environment-specific QTL for seed mass and germination timing in seeds matured under a low R:FR. Lastly, in chapter 3, I investigate if and how phytochrome photoreceptor genes mediate the effects of maternal R:FR on progeny germination. My results suggest that all 5 phytochrome genes in A. thaliana partially mediate progeny germination response to maternal R:FR, and I identify novel roles for individual phytochrome loci in this response. As a whole, this research provides insight into the extent that maternal effects in competitive environments are adaptive and partially elucidates the genetic basis of maternal effects.
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    Analysis of Proteome-scale Protein Turnover in Arabidopsis thaliana Seedlings and Its Application to the Plant Heat Stress Response
    (2015-08) Fan, Kai-Ting
    Protein turnover, the balance between protein synthesis and degradation, is an important aspect of the regulation of cellular processes for organisms as they respond to developmental or environmental cues. How proteome turnover will be influenced in plants when exposed to abiotic stress, especially moderately high temperature, has not been studied systematically. The study of protein turnover in plants, contrary to that of rapidly growing unicellular organismal cultures, is made more complicated by the high degree of amino acid recycling, which results in significant transient isotope incorporation distributions that must be dealt with computationally for high throughput analysis to be practical. In this study, an algorithm implemented in the statistical programing language R, ProteinTurnover, was developed to calculate protein turnover with transient stable isotope incorporation distributions in a high-throughput automated manner using high resolution mass spectrometry and proteomic analysis of stable isotopically labeled plant material. ProteinTurnover extracts isotopic distribution information for peptides identified by tandem MS from raw MS datasets of either isotopic label dilution or incorporation experiments. Variable isotopic distributions were modeled by maximum likelihood estimation using binomial or beta-binomial distributions to (1) unlabeled, (2) newly-synthesized (partially-labled) and (3) fully-labeled peptide distributions. The distribution abundance proportions of old to newly synthesized peptide distributions were calculated using quantities derived from the models. Half-lives and turnover rates were calculated by fitting the change in the distribution abundance prorportions over time to a first-order decay function using non-linear regression. Using ProteinTurnover, turnover rates of hundreds of proteins were measured in soluble, organellar, and microsomal fractions of Arabidopsis seedling roots, using isotopic incorporation. In a second study, ProteinTurnover was used to measure changes in proteome turnover in soluble, organelle, and microsomal fraction of Arabidopsis seedling shoots or roots comparing 22°C and 30°C growth conditions. A total of 571 proteins as exhibiting significant changes in turnover rate in response to elevated temperature were identified in Arabidopsis seedling tissues. In general, soluble proteins extracted from root tissue displayed relatively smaller changes in turnover. Proteins involved in photorespiration, protein folding, stress response, secondary metabolism, and redox signaling pathways exhibited the greatest changes in turnover under heat stress.
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    Metabolomics study on Arabidopsis thaliana abiotic stress responses for priming, recovery, and stress combinations
    (2018-04) Xu, Yuan
    Temperature, water, and light are three stress factors that have major influences on plant growth, development, and reproduction. Plants can be primed to an acclimated state by a prior mild stress to enhance their resistance to future stress. ‘Priming’ is related to plant stress ‘memory’ during recovery. Plants may need to balance between keeping the memory for enhanced stress defense and resetting for maximum growth and development during recovery. In the field, plants are more often to encounter a combination of different abiotic stresses rather than a specific single stress condition. Plant responses to a combination of stresses may exhibit quite unique defense and acclimation responses as compared to the response elicited by each individual stress, which should not be simply considered as the sum of the two different stresses. However, the simultaneous occurrence of multiple stress events is rarely studied experimentally, especially by metabolomics methods. Metabolomics, the comprehensive, quantitative and qualitative analysis of small molecules, is an emerging 'omics' platform that is an important next-generation systems biology approach. By providing an instantaneous “snapshot” of metabolic processes that occur in an organism, metabolomics can potentially provide insightful molecular mechanism information to questions about physiological function in complex biological systems. The objective of this thesis research was to use both untargeted and targeted metabolomics approaches to investigate plant shared and unique metabolic features in responses to single as well as multiple abiotic stresses, the priming effect of temperature stresses, plant memory during recovery phase, and the relationships between combined stress with each of individual stresses. An ultra-high pressure liquid chromatography-high resolution mass spectrometry (UHPLC-HR-MS)-based metabolomics approach was utilized. In chapter two, a metabolomics study on Arabidopsis thaliana 11-day-old seedling’s abiotic stress responses including heat (basal and acquired), cold (basal and acquired), drought and high light with 2-day-recovery was performed using a standardized reference system. In chapter three, Arabidopsis thaliana 11-day-old seedlings that were induced by the combination of different abiotic stresses including heat, cold, drought, salinity, and high light, that mimics field environment was studied. From this thesis research, a number of potential stress signatures determined from the untargeted analysis were identified, quantified and clustered by stress response patterns. Central metabolism were found to undergo a complex regulatory process in response to stress. Shared and unique metabolic signatures were identified across different abiotic single and combined stresses. The majority of stress signatures clustered together and exhibited shared response patterns. However, cysteine, glutathione, and maltose showed unique and dramatic patterns, demonstrating large changes in glutathione biosynthesis, glutathione oxidation, and starch degradation. The results showed that only two combined stresses, including high light x cold and cold x salinity, had metabolic effects that reflected both of their constituent single stresses. Most combined stresses had one dominant stress that had a defining impact on the plant metabolic profile. Drought stress is the dominant stress for all of its stress combinations. Two combined stresses, including high light x heat and high light x salinity, showed unique metabolic stress response patterns that are not similar to any of their individual stresses. Most of these metabolic features were specifically changed only in the combined stress, which should thus be considered as novel stress conditions. In summary, this work utilized metabolomics to study plant priming effects, recovery processes, and combined stress responses. It led to an improved understanding of how plants respond to abiotic stresses and may support subsequent studies on plant abiotic stress metabolic flux analyses.
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    MNC1 Negatively Regulates Nectar Production through Auxin and Jasmonic Acid Response Pathways in Arabidopsis thaliana
    (2014-11) Jia, Mengyuan
    Many flowering plants offer a reward for pollinators in the form of nectar. Despite the central role of pollination in reproduction of plants and the considerable amount of energy a plant devotes to produce nectar, little is known of the molecular mechanism of nectar production and its regulation. Previous reports have suggested a significant role for the plant hormone auxin in regulating nectar production. Recent transcriptome studies have made it possible to focus research on several nectary-specific candidate genes with putative roles in the auxin response. In Arabidopsis thaliana this includes a gene termed MEDIAN NECTARY CUPIN 1 (MNC1; At1g74820), which is highly expressed in median nectaries. MNC1 silenced mutants (mnc1) showed more nectar production and increased auxin response activity while MNC1 overexpresser mutant (MNC1 T6) showed significantly less nectar production and less auxin response activity in nectaries. A comparative sequence analysis of proteins with known function shows that MNC1 is a germin-like protein belonging to the RmlC-like cupins superfamily. MNC1 also has a conserved zinc binding domain with known Auxin Binding Protein1. Thus, we hypothesize that MNC1 negatively regulates nectar production, likely through an auxin dependent pathway. PIN6 (At1g77110), an auxin transporter family protein, has been reported to be an auxin transporter localized to the ER modulating cytoplasmic free auxin concentration in nectaries. Arabidopsis thaliana mutant lines with different combinations of crossed target genes were used to understand the feedback mechanism of auxin, nectar production, PIN6, and MNC1 protein behind nectar regulation and production. Transformed Escherichia coli and Pichia pastoris, a methylotrophic yeast species, expressing MNC1 protein were employed for studying its biochemical nature, including auxin binding activity. Jasmonic acid (JA) was also suggested to be required for nectar production, with possible crosstalk to auxin in regulation of nectar production. COI1-independent JA response pathway was found to regulate nectar production by altering the expression of nectary-specific genes such as SWEET9, a sucrose transporter required for nectar production, CWINV4, a cell wall invertase required for nectar production, and MNC1. A potential auxin-JA crosstalk mechanism was constructed based on results in this study and previous studies.
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    A Sucrose Transporter and Proper Hormone Response are Essential for Nectary Function in the Brassicaceae
    (2013-12) Klinkenberg, Peter
    Nectar is a reward presented by flowers to attract pollinators to facilitate fertilization. While much is known about the chemical make-up of nectar, little is known about the mechanisms of production and secretion of this pollinator attractant. SWEET9, a nectary enriched gene, was demonstrated to be vital for nectar production in two Brassicaceae species, Arabidopsis thaliana and Brassica rapa as determined by SWEET9pro::GUS histochemical staining and RT-PCR,. The Arabidopsis mutant atsweet9-3, produced no nectar and three independent mutants in B. rapa, (brsweet9-1, -2, and -3) similarly produced no nectar. All four mutants had normal nectary morphology. Transporter assays of SWEET9 expressed in Xenopus oocytes displayed sucrose uniport activity, suggesting a direct role in sugar export. To determine a potential mechanism for the regulation of SWEET9 expression, the plant hormone jasmonic acid (JA) was investigated because it was previously implicated in nectary function. Indeed, JA synthesis (aos-2 and dad1) and response (myb21-4) mutants displayed an absence of floral nectar, in addition to male-sterility. When treated with exogenous MeJA, aos-2 and dad1 mutants regained their nectar production and fertility, while the myb21-4 transcription factor mutant was insensitive to treatment. Significantly, SWEET9 expression was strongly decreased in the JA response mutant myb21-4, in addition to several other genes known to be important in nectary function. For example, all three JA mutants studied displayed decreased expression of PIN6, a nectary enriched gene required for proper auxin homeostasis in the nectaries of Arabidopsis. Additionally auxin response was lost in the JA synthesis mutant aos-2, suggesting an important hormonal crosstalk between JA and auxin. To further investigate the link between JA and the auxin response in nectaries, mutants with altered endogenous auxin levels were created. Mutants with decreased nectary auxin produced 50% less nectar than wild-type plants and had reduced auxin response. Cumulatively, these results identify SWEET9 as a sucrose transporter required for nectar production and that JA plays a major role in the regulation of nectary-specific genes and other hormonal pathways important for nectar production.