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Bypassing Iron Storage In Endodermal Vacuoles Rescues The Iron Mobilization Defect In The Natural Resistance Associated-Macrophage Protein3natural Resistance Associated-Macrophage Protein4 Double Mutant, Viviane Mary, Magali Schnell Ramos, Cynthia Gillet, Amanda L. Socha, Jerome Giraudat, Astrid Agorio, Sylvain Merlot, Colin Clairet, Sun A. Kim, Tracy Punshon, Mary Lou Guerinot, Sebastien Thomine

Dartmouth Scholarship

To improve seed iron (Fe) content and bioavailability, it is crucial to decipher the mechanisms that control Fe storage during seed development. In Arabidopsis (Arabidopsis thaliana) seeds, most Fe is concentrated in insoluble precipitates, with phytate in the vacuoles of cells surrounding the vasculature of the embryo. NATURAL RESISTANCE ASSOCIATED-MACROPHAGE PROTEIN3 (AtNRAMP3) and AtNRAMP4 function redundantly in Fe retrieval from vacuoles during germination. When germinated under Fe-deficient conditions, development of the nramp3nramp4 double mutant is arrested as a consequence of impaired Fe mobilization. To identify novel genes involved in seed Fe homeostasis, we screened an …

Anaerobic Detoxification Of Acetic Acid In A Thermophilic Ethanologen, A Joe Shaw, Bethany B. Miller, Stephen R. Rogers, William Robert Kenealy, Alex Meola, Ashwini Bhandiwad, W Ryan Sillers, Indraneel Shikhare, David Hogsett, Christopher Herring

Dartmouth Scholarship

The liberation of acetate from hemicellulose negatively impacts fermentations of cellulosic biomass, limiting the concentrations of substrate that can be effectively processed. Solvent-producing bacteria have the capacity to convert acetate to the less toxic product acetone, but to the best of our knowledge, this trait has not been transferred to an organism that produces ethanol at high yield. We have engineered a five-step metabolic pathway to convert acetic acid to acetone in the thermophilic anaerobe Thermoanaerobacterium saccharolyticum.

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Allelic Polymorphism Of Gigantea Is Responsible For Naturally Occurring Variation In Circadian Period In Brassica Rapa, Qiguang Xie, Ping Lou, Victor Hermand, Rashid Aman

Dartmouth Scholarship

GIGANTEA (GI) was originally identified by a late-flowering mutant in Arabidopsis, but subsequently has been shown to act in circadian period determination, light inhibition of hypocotyl elongation, and responses to multiple abiotic stresses, including tolerance to high salt and cold (freezing) temperature. Genetic mapping and analysis of families of heterogeneous inbred lines showed that natural variation in GI is responsible for a major quantitative trait locus in circadian period in Brassica rapa. We confirmed this conclusion by transgenic rescue of an Arabidopsis gi-201 loss of function mutant. The two B. rapa GI alleles each fully rescued the …

Myb10 And Myb72 Are Required For Growth Under Iron-Limiting Conditions, Christine M. Palmer, Maria N. Hindt, Holger Schmidt, Stephan Clemens, Mary Lou Guerinot

Dartmouth Scholarship

Iron is essential for photosynthesis and is often a limiting nutrient for plant productivity. Plants respond to conditions of iron deficiency by increasing transcript abundance of key genes involved in iron homeostasis, but only a few regulators of these genes have been identified. Using genome-wide expression analysis, we searched for transcription factors that are induced within 24 hours after transferring plants to iron-deficient growth conditions. Out of nearly 100 transcription factors shown to be up-regulated, we identified MYB10 and MYB72 as the most highly induced transcription factors. Here, we show that MYB10 and MYB72 are functionally redundant and are required …

Arabidopsis Bhlh100 And Bhlh101 Control Iron Homeostasis Via A Fit-Independent Pathway, Alicia B. Sivitz, Victor Hermand, Catherine Curie, Grégory Vert

Dartmouth Scholarship

Iron deficiency induces a complex set of responses in plants, including developmental and physiological changes, to increase iron uptake from soil. In Arabidopsis, many transporters involved in the absorption and distribution of iron have been identified over the past decade. However, little is known about the signaling pathways and networks driving the various responses to low iron. Only the basic helix–loop–helix (bHLH) transcription factor FIT has been shown to control the expression of the root iron uptake machinery genes FRO2 and IRT1. Here, we characterize the biological role of two other iron-regulated transcription factors, bHLH100 and bHLH101, in iron homeostasis. …

The Role Of Cax1 And Cax3 In Elemental Distribution And Abundance In Arabidopsis Seed, Tracy Punshon, Kendall Hirschi, Jian Yang, Antonio Lanzirotti, Barry Lai, Mary Lou Guerinot

Dartmouth Scholarship

The ability to alter nutrient partitioning within plants cells is poorly understood. In Arabidopsis (Arabidopsis thaliana), a family of endomembrane cation exchangers (CAXs) transports Ca²⁺ and other cations. However, experiments have not focused on how the distribution and partitioning of calcium (Ca) and other elements within seeds are altered by perturbed CAX activity. Here, we investigate Ca distribution and abundance in Arabidopsis seed from cax1 and cax3 loss-of-function lines and lines expressing deregulated CAX1 using synchrotron x-ray fluorescence microscopy. We conducted 7- to 10-μm resolution in vivo x-ray microtomography on dry mature seed and 0.2-μm resolution x-ray …

Mir319a Targeting Of Tcp4 Is Critical For Petal Growth And Development In Arabidopsis, Anwesha Nag, Stacey King, Thomas Jack

Dartmouth Scholarship

In a genetic screen in a drnl-2 background, we isolated a loss-of-function allele in miR319a (miR319a¹²⁹). Previously, miR319a has been postulated to play a role in leaf development based on the dramatic curled-leaf phenotype of plants that ectopically express miR319a (jaw-D). miR319a¹²⁹ mutants exhibit defects in petal and stamen development; petals are narrow and short, and stamens exhibit defects in anther development. The miR319a¹²⁹ loss-of-function allele contains a single-base change in the middle of the encoded miRNA, which reduces the ability of miR319a to recognize targets. Analysis of the expression patterns of the …

Disruption Of Osysl15 Leads To Iron Inefficiency In Rice Plants, Sichul Lee, Jeff C. Chiecko, Sun A. Kim, Elsbeth L. Walker, Youngsook Lee, Mary Lou Guerinot, Gyhheung An

Dartmouth Scholarship

Uptake and translocation of metal nutrients are essential processes for plant growth. Graminaceous species release phytosiderophores that bind to Fe³⁺; these complexes are then transported across the plasma membrane. We have characterized OsYSL15, one of the rice (Oryza sativa) YS1-like (YSL) genes that are strongly induced by iron (Fe) deficiency. The OsYSL15 promoter fusion to β-glucuronidase showed that it was expressed in all root tissues when Fe was limited. In low-Fe leaves, the promoter became active in all tissues except epidermal cells. This activity was also detected in flowers and seeds. The OsYSL15:green …

Chloroplast Fe(Iii) Chelate Reductase Activity Is Essential For Seedling Viability Under Iron Limiting Conditions, Jeeyon Jeong, Christopher Cohu, Loubna Kerkeb, Marinus Pilon, Erin L. Connolly, Mary Lou Guerinot

Dartmouth Scholarship

Photosynthesis, heme biosynthesis, and Fe-S cluster assembly all take place in the chloroplast, and all require iron. Reduction of iron via a membrane-bound Fe(III) chelate reductase is required before iron transport across membranes in a variety of systems, but to date there has been no definitive genetic proof that chloroplasts have such a reduction system. Here we report that one of the eight members of the Arabidopsis ferric reductase oxidase (FRO) family, FRO7, localizes to the chloroplast. Chloroplasts prepared from fro7 loss-of-function mutants have 75% less Fe(III) chelate reductase activity and contain 33% less iron per microgram of chlorophyll than …

Variation In Molybdenum Content Across Broadly Distributed Populations Of Arabidopsis Thaliana Is Controlled By A Mitochondrial Molybdenum Transporter (Mot1), Ivan Baxter, Balasubramaniam Muthukumar, Hyeong Cheol Park, Peter Buchner, Brett Lahner, John Danku, Keyan Zhao, Joohyun Lee, Malcolm J. Hawkesford, Mary Lou Guerinot, David E. Salt

Dartmouth Scholarship

Molybdenum (Mo) is an essential micronutrient for plants, serving as a cofactor for enzymes involved in nitrate assimilation, sulfite detoxification, abscisic acid biosynthesis, and purine degradation. Here we show that natural variation in shoot Mo content across 92 Arabidopsis thaliana accessions is controlled by variation in a mitochondrially localized transporter (Molybdenum Transporter 1 - MOT1) that belongs to the sulfate transporter superfamily. A deletion in the MOT1 promoter is strongly associated with low shoot Mo, occurring in seven of the accessions with the lowest shoot content of Mo. Consistent with the low Mo phenotype, MOT1 expression in low Mo accessions …