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Terpenes are secondary metabolites produced by plants and they have promising roles in plant defense and pharmaceuticals. They are synthesized by terpene synthases and these enzymes are part of a complex plant metabolic pathway. Diterpene biosynthesis requires co-expression of class II and class I diterpene synthases (diTPSs) to convert geranylgeranyl diphosphate (GGPP), the common precursor, into a C20 intermediate substrate. These substrates then use cytochrome p450s (CYPs) as their final steps to form diterpene scaffolds. CYPs are monooxygenases that change the redox status of their substrates into final diterpene products. Medicago truncatula was used as my model organism to investigate how legumes synthesize these secondary metabolites to contribute to crop defense improvement in the future. Seven diTPSs - MtTPS17, MtTPS18, MtTPS19, MtTPS37, MtTPS38, MtTPS39, and MtTPS40 - in M. truncatula have been identified. MtTPS38 was found to produce ent-CPP and MtTPS37 used ent-CPP to yield ent-kaurene. Combinatorial expression showed that MtTPS38 and MtTPS37 react together to produce ent-kaurene, a precursor for an important plant hormone gibberellin (GA). CYPs have also been discovered to be clustered around MtTPS19, suggesting the possibility of MtTPS19 utilizing these CYPs for downstream reactions.

京都大学 / 新制・課程博士 / 博士(人間・環境学) / 甲第23263号 / 人博第978号 / 新制||人||232(附属図書館) / 2020||人博||978(吉田南総合図書館) / 京都大学大学院人間・環境学研究科相関環境学専攻 / (主査)教授 瀬戸口 浩彰, 教授 加藤 眞, 教授 市岡 孝朗 / 学位規則第4条第1項該当 / Doctor of Human and Environmental Studies / Kyoto University / DFAM

Eastern hemlock hosts the hemlock woolly adelgid, an introduced sap-feeding insect that causes rapid deterioration of the host. Like most conifers, eastern hemlock produces a variety of constitutive and induced defenses, primarily terpenoids. To explore the relationship of terpenoid defenses with adelgid infestations, we artificially infested hemlocks at a forest site and a plantation site, and compared their terpenoid concentrations to those in control trees. Infested trees showed lower terpenoid concentrations than control trees, suggesting that eastern hemlock not only fails to induce production of terpenoids in response to adelgid infestation, but becomes less able to produce carbon-based defenses due to loss of carbon resources to the adelgid. Greater light intensity may account for consistently higher terpenoid concentrations at the plantation site, supporting the explanation that carbon limitation restricts terpenoid production. Recent studies have identified a small number of individual eastern hemlock trees that demonstrate relative resistance to the hemlock woolly adelgid. We compared concentrations of terpenoids in susceptible and relatively resistant trees, both in the forest and in propagated cuttings in a common-garden setting. Terpenoid concentrations were higher in twig tissue of resistant versus susceptible trees, across six sampling dates and at both sites. Because the common-garden cuttings were free of herbivores, the higher terpenoid concentrations are interpreted as a constitutive defense. Increased levels of monoterpenes and sesquiterpenes imply an overall increase in the input of carbon precursors to both terpenoid synthesis pathways. This result suggests either an altered growth-defense balance favoring allocation of carbon resources towards production of defenses, or overall greater carbon availability in growing twig tissue of adelgid-resistant eastern hemlock individuals. We contribute detailed terpenoid data to the study of the eastern hemlock – hemlock woolly adelgid system. Our solvent extraction method permits us to examine needle and twig tissues separately, capture minor components at low concentrations, and focus on stored rather than volatilized terpenoids. By relating terpenoid concentrations to insect densities, we explore the relationships of tentatively defensive chemistry to insect population dynamics. The question remains which terpenoids, if any, directly affect hemlock woolly adelgid and what role phenols may play in the system.

Lignocellulosic biomass is one of the most abundant raw materials on earth that can be utilized to created carbon-neutral biofuels as a replacement for conventional fossil fuels. In order to create ideal energy crops, the regulation and deposition of cell wall polysaccharides must first be fully understood. Improved understanding of cell wall regulation will enable selection of traits that can optimize biofuel feedstocks. Herein, I utilize the grass model system Brachypodium distachyon in order to understand the transcriptional regulation of secondary cell wall deposition. Gene expression profiling was used to elucidate transcription factors that regulate secondary cell wall biosynthesis. Through this method, WALL REGULATOR INTERACTING bHLH (WRIB) was identified and its role as a secondary cell wall regulator was tested. Yeast-one- and yeast-two-hybrid assays showed that WRIB is capable of binding to promoters of secondary cell wall biosynthesis genes, as well as interacting with known secondary cell wall transcription factor proteins and also Phytochrome B. These results suggest that WRIB plays an important role in the secondary cell wall regulatory network and could perhaps be modulated by Phytochrome B. Discovery of this novel and interesting gene furthers the overall understanding of secondary cell wall development with the goal of improving our ability to engineer biofuel feedstocks.

As the population continues to rise, there becomes an ever-increasing need for sustainable food production not only to produce enough food but also to ensure the feasibility of our farmland for years to come. In an effort to curb this problem, nanotechnology is an up-and-coming strategy that acts as a sustainable method of boosting a crop’s growth and yield, especially the use of nanoscale sulfur. The work included in this thesis is an investigation into the question of whether this technology has the potential to increase these parameters in Spring wheat var. Louise (Triticum aestivum L.). In order to answer this question, several application methods including soil amendment, foliar spray, and seed priming were utilized and the results of which are presented below. Methods used to compare each of the treatments include recording different growth parameters such as the Soil Plant Analysis Development (SPAD) value and ethanol assays for the chlorophyll content along with the linear electron flow and Fv/Fm (a sensitive indicator of plant photosynthetic performance or maximum quantum yield of photosystem II) values to assess plant stress. Short-term and maturity experiments were performed and after harvest, parameters such as dry biomass (straw and root), tiller number, flag leaf length, ear length, harvest index, and seed yield were recorded to further assess whether nano sulfur has beneficial impacts on wheat. The goal of this research is to provide additional insights into the use of nanosulfur in wheat agriculture and act as a supplement to other research being performed in this field. From the results, it was found that when plants were treated with the sulfur treatments using the foliar spray application method, there were many increases in the parameters being investigated for increased growth and yield. Agronomic parameters included the flag leaf length, dry straw weight, and seed weight per plant while photosynthetic parameters included SPAD, Fv/Fm, and LEF. At all three concentrations (50, 100, and 200 ppm) foliar applications, the nanosulfur (NS)and nanosulfur coated with stearic acid (NS SA) and sulfate showed a significant increase in chlorophyll 6.3-10.7%), dry biomass (7.9-14.6%), Fv/FM (2.8-3.0%) whereas the bulk sulfur was less effective. Further, 50 ppm, there are highly significant increases across all treatments (BS, sulfate, NS, NS SA, and NS PVP) with 26.9%, 26.1%, 24.5%, 18.4%, and 16.3% increases, respectively, compared to the control group. At 100 ppm application rates, there are highly significant increases in BS (24.8%), sulfate (29.5%), NS SA (15.3%), and the NS treatment (11.2%). When 200 ppm was used, there were highly significant results in BS (34.0%), sulfate (20.9%), NS SA (53.2%), and NS PVP (42.8%) treatment groups, while plants treated with NS SA had a slight but significant increase (13.5%) when compared to the control. From these, it was shown that the sodium sulfate and stearic acid coated nanosulfur had the most consistent significant increases in these parameters, leading to this conclusion. For soil amendment assay, the results were not very conclusive but overall NS and NS SA group showed significant increases in the number of tillers and the length of primary ears whereas BS and sulfate treatments caused a significant decrease in these parameters. From this research, the data that resulted from the soil amendment and seed priming experiments were somewhat inconclusive, indicating that additional research is required to further understand the mechanism for these two application methods.

Summers are expected to continue to increase in heat/dryness in the Northeast, causing issues pertaining to forage production during the summer to worsen. Many pastures grow cool season grasses, even during the summer. These grasses enter a dormant period and slowdown in production during the months of July and August, leading to what is referred to as “summer slump”. Some farms grow corn silage during the summer, and while corn silage is a valuable crop, its cultivation often does not support soil biology. This research addresses solutions for both summer slump foraging and more sustainable silage. Summer annuals grow more efficiently during the summer and can produce better quality forage compared to winter grasses. Pearl Millet and Sudangrass were evaluated at seed percentages 0-100%. Biomass of each grass was evaluated by cutting a 2x3 ft section on a bi-weekly basis to establish how the treatments vary over time by seeding ratio and type of warm-season grass. Two separate cuts evaluated yield, quality, and regrowth. Another cut looked at ensiling success and quality of Pearl millet and Sudangrass. Results showed both forage species had similar and comparable quality to cool-season grasses. With how much more Sudangrass produces in yield and the little difference in forage quality compared to Pearl millet, Sudangrass would make a good replacement for cool-season grasses. Pearl millet and Sudangrass can be ensiled successfully and have competitive forage quality compared to corn silage.

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Master of Science / Department of Agronomy / William T. Schapaugh Jr / Crops research moving forward faces many challenges to improve crop performance. In breeding programs, phenotyping has time and economic constraints requiring new phenotyping techniques to be developed to improve selection efficiency and increase germplasm entering the pipeline. The objectives of these studies were to examine the changes in spectral reflectance with soybean breeding from 1923 to 2010, evaluate band regions most significantly contributing to yield estimation, evaluate spectral reflectance data for yield estimation modeling across environments and growth stages and to evaluate the usefulness of spectral data as an optimized phenotyping technique in breeding programs. Twenty maturity group III (MGIII) and twenty maturity group IV (MGIV) soybeans, arranged in a randomized complete block design, were grown in Manhattan, KS in 2011 and 2012. Spectral reflectance data were collected over the growing season in a total of six irrigated and water- stressed environments. Partial least squares and multiple linear regression were used for spectral variable selection and yield estimation model building. Significant differences were found between genotypes for yield and spectral reflectance data, with the visible (VI) having greater differences between genotypes than the near-infrared (NIR). This study found significant correlations with year of release (YOR) in the VI and NIR portions of the spectra, with newer released cultivars tending to have lower reflectance in the VI and high reflectance in the NIR. Spectral reflectance data accounted for a large portion of variability for seed yield between genotypes using the red edge and NIR portions of the spectra. Irrigated environments tended to explain a larger portion of seed yield variability than water-stressed environments. Growth stages most useful for yield estimation was highly dependent upon the environment as well as maturity group. This study found that spectral reflectance data is a good candidate for exploration into optimized phenotyping techniques and with further research and validation datasets, may be a suitable indirect selection technique for breeding programs.