Theses and Dissertations at Montana State University (MSU)
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Item Effect of the WRKY76 transcription factor on starch biosynthesis and plant growth(Montana State University - Bozeman, College of Agriculture, 2016) Estabrooks, Hannah Margaret; Chairperson, Graduate Committee: Jack MartinStarch is an important contributor to plant growth as excess photosynthate is stored in leaves as starch during the day to be mobilized at night and re-synthesized in sink tissues. Starch is also the principal constituent of cereal seeds and its variation greatly influence crop yields. The starch pathway is complex and its regulation is not fully understood. Transcription Factors (TFs) are known to act as master regulators of whole biosynthetic pathways and the work presented here was aimed at gaining a better understanding of starch production in leaves by identifying a TF which specifically regulates the leaf starch biosynthetic pathway. Leaf starch levels are regulated in part by ADP-glucose pyrophosphorylase (AGPase), the rate limiting step of starch biosynthesis. Transgenic rice event (NR16+) with increased leaf AGPase activity (due to overexpression of the AGPase large and small subunit transgenes Sh2r6hs and Bt2) was subjected to RNA-sequencing. The results indicated that the leaf specific AGP transgene, which increased leaf starch, also had upregulation of the WRKY76 TF. Another regulatory protein, F-Box, was chosen as a candidate due to the F-box family's involvement in plant development. The current study examines the potential of these gene products for increasing starch biosynthesis in leaves via leaf specific overexpression. Results indicate that overexpression of WRKY76 increases leaf starch an average of 39% at both the one month and anthesis growth stages in comparison to the Varietal Control Nipponbare. WRKY76 transgenic lines have enhanced phenotype with an improved harvest index due to biomass and immature panicles trending down by 4% and 21% respectively, while seed weight trended 12% higher. Events overexpressing WRKY76 were also found to upregulate important starch biosynthetic and carbon metabolism genes including AGPL1, AGPS2, SSIIIb, GBSII, Rbcs, PRK, and GS2 as well as leading to a general upregulation of leaf tissue carbohydrates. Events 1, 2, and 12 additionally had on average 13% increased photosynthetic rate at the one month growth stage. The findings of this study support WRKY76 as a dynamic regulator of the starch biosynthetic pathway conferring more efficient carbon assimilation leading to an increased harvest index.Item Relationship of ADP-glucose pyrophosphorylase to the regulation of starch accumulation in wheat leaves infected with Puccinia striiformis West(Montana State University - Bozeman, College of Agriculture, 1970) MacDonald, Paul WilliamItem Starch utilization, root bud correlative inhibition, and endogenous indole-3-acetic acid levels in leafy spurge (Euphorbia esula L.)(Montana State University - Bozeman, College of Agriculture, 1986) Nissen, Scott Jay; Chairperson, Graduate Committee: Michael Foley.Leafy spurge (Euphorbia esula L.) is a rapidly spreading perennial rangeland weed which continues to persist and spread despite increased efforts at biological and chemical control. The persistence of leafy spurge can be traced directly to the plant’s root carbohydrate reserves and its effective means of vegetative reproduction. Research was initiated to examine aspects of these two important survival mechanisms . Utilization of leaf, stem, root and latex starch was monitored in leafy spurge plants during a 52 day light starvation period. Leaf, stem and root starch levels decreased rapidly in light starved plants; however, detectable levels of starch were present even after 52 days without light. Latex starch levels did not change significantly. Amylase activity was present in the latex; however, latex starch granules were found to be resistant to enzymatic hydrolysis. Results indicated that latex starch granules do not function as a source of utilizable carbohydrate. Root buds were found to be quiescent during most of the growing season due to correlative inhibition rather than innate dormancy. Innate dormancy occurred when plants were in full flower; however, elongation could be stimulated by chilling intact plants for 8 days at 4 C. Exogenous applications of indole-3-acetic acid and napthalene-acetic acid at concentrations of 10 -3 M and 10 -5 M respectively, completely inhibited elongation of excised root buds. Significant increases in root bud elongation were produced by 1 mM 2,3,5-tri-iodobenzoic acid applied to stem and root tissue. These data provide evidence for the involvement of IAA in correlative control of root bud growth. Primary root and root bud endogenous IAA levels were determined at three phenologic stages: vegetative, full flower and post flower. Free IAA levels were highest in root bud of full flowering plants which were found in previous studies to have a diminished capacity to elongate. Levels of conjugated IAA increased during phenologic development. Primary root free IAA levels did not appear related to lowered root bud elongation during full flower.Item Influence of waxy and high-amylose starch genes on the composition of barley and the cholesterolemic and glycemic responses in chicks and rats(Montana State University - Bozeman, College of Agriculture, 1992) Xue, Qi; Co-chairs, Graduate Committee: Rosemary K. Newman and Charles F. McGuireItem Transitory leaf starch is an important determinant of plant yield(Montana State University - Bozeman, College of Agriculture, 2011) Schlosser, Alanna Jane; Chairperson, Graduate Committee: Michael J. Giroux.Efficient allocation of photoassimilates from source to sink tissues is important for optimal plant growth and yield as relative source and sink strength drives growth potential of plant organs. A common method aimed at improving plant yield has been to modify enzymes important to storage compound biosynthesis in sink tissues such as seeds. As the rate limiting step in starch biosynthesis, ADP-glucose pyrophosphorylase (AGPase) has received much attention in this regard. Previously, overexpression of AGPase in seeds resulted in an enhanced yield phenotype in which both plant yield and biomass were increased. However, yield advantages were only observed under nonlimiting environmental resources. The objective of these studies was to 1) determine the importance of native leaf starch levels to the productivity and growth of maize and 2) target source strength by overexpressing AGPase in rice leaves. To determine the importance of native leaf starch levels in maize, field trials of BC 4F 2:3 plants segregating for the presence or absence of the agps-m1 mutation and leaf starch were conducted in Citra, Florida. The results clearly demonstrate the importance of normal leaf starch levels to maize productivity. The starchless agps-m1 plants were 6 to 13 cm shorter, flowered 2 to 3 days later, and had 30 percent lower seed yield than their wild type sisterlines. The impact of increased AGPase in rice leaves was then tested by overexpressing AGPase in rice leaves. Two expression constructs were used to transform rice cultivar Nipponbare, each containing a modified form of the maize endosperm AGPase large subunit sequence, Sh2r6hs, as well as the small subunit sequence, Bt2. Expression of the transgenes was under control of either the rice leaf AGPase small subunit promoter, Ags1, or native rice RuBisCO small subunit promoter, RBC. Expression of the transgenes under the RBC promoter is associated with significantly increased plant biomass. Our results indicate that it is possible to increase plant yield without increasing the rate of photosynthesis. Further, it indicates the possibility of manipulating plant yield through increasing AGPase activity in leaf tissue.