Plant Science & Landscape Architecture Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2797
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Item The MEIOTIC PROPHASE AMINOPEPTIDASE 1 regulates polyploidy in Arabidopsis thaliana(2017) Wattarantenne, Kasuni Vishwaprabha; Peer, Wendy A; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Growth and development in plants is dependent on cellular functions such as cell cycle progression. M1 aminopeptidases have been shown to regulate mitosis and meiosis in animals. MEIOTIC PROPHASE AMINOPEPTIDASE M1 (MPA1) in Arabidopsis thaliana was previously shown to regulate cell cycle progression during prophase I in meiosis I in both female and male gametophytes and be essential for homologous recombination. mpa1 homozygous embryos are lethal due to chromosome de-synapsis resulting in uneven distribution of chromosomes in daughter cells and massive decrease in homologous crossovers reduces independent assortment. Here, I show that MPA1 is a soluble protein and is expressed throughout the seedling: in the primary root, hypocotyl, cotyledons, petioles and root and shoot apical meristem. I isolated and characterized four mpa1 alleles, and I showed that MPA1 loss-of-function mutants exhibited three significant phenotypes corresponding to development in seedlings and adult plants in Arabidopsis: non-disjunction in mitotic cells, altered polyploidy, and temporary arrest of primary root growth during seedling establishment.Item INVESTIGATION OF ARABIDOPSIS TSO1, A REGULATOR OF CELL PROLIFERATION AND DIFFERENTIATION(2017) WANG, WANPENG; Liu, Zhongchi; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Multicellular eukaryotic organisms build complex body structures from a single cell. Through coordinated cell proliferation and differentiation, the collective behavior of cells forms organs that achieve physiological functions. Underlying the developmental processes are the molecular machineries that integrate cell cycle regulation with cell fate acquisition. While animal organogenesis occurs early during embryogenesis, plants maintain pluripotent stem cells at the growing tips (meristems) and generate organs iteratively throughout lifespan. The amazing ability to balance stem cell self-renewal and differentiation underlies the extreme longevity of some plants species. Despite the differences, common mechanisms exist across plant and animal developmental regulation. Understanding both unique and common mechanisms of plant development has broad implications on basic science as well as agriculture and medicine. The Arabidopsis TSO1 gene is a regulator of cell proliferation and differentiation at the shoot and root meristems. TSO1 encodes a CXC domain protein and its animal homologs encode core components of a cell cycle regulatory complex, the DREAM complex. To investigate TSO1 function and identify factors that act together with TSO1, I carried out two genetic screens for suppressors and enhancers of tso1 mutants. I discovered that loss-of-function mutations in MYB3R1, which encodes the Arabidopsis ortholog of human B-Myb, can suppress tso1 mutant defects at both the shoot and root meristems. In tso1-1 mutant, MYB3R1 is over and ectopically expressed at the shoot and root meristems. Furthermore, MYB3R1 phospho mimic enhanced the tso1-3 phenotype, indicating that hyper-active MYB3R1 may mediate the tso1-1 phenotype. TSO1 physically interacts with MYB3R1 and likely forms a plant DREAM-like complex that operates in the plant meristems to balance cell proliferation with differentiation. A gain-of-function mutation of a HD-ZIP III transcription factor, REVOLUTA (REV), was identified as an enhancer of tso1 mutants. TSO1 directly represses REV transcription to balance adaxial and abaxial polarity of lateral organs and maintains the shoot apical meristem. This genetic and molecular interaction between TSO1 and the adaxial factor REV presents an integration point of cell cycle, lateral organ polarity, and meristem regulation. Together, our findings demonstrate a cell cycle regulatory module conserved across plants and animals and describe its integration into plant specific developmental context.Item IDENTIFICATION AND CHARACTERIZATION OF IAA OXIDASES AND THEIR ROLE IN IAA HOMEOSTATIC REGULATION IN ARABIDOPSIS(2016) Zhang, Jun; Peer, Wendy Ann; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Auxin is a crucial plant hormone that shapes and directs plant growth. Indole-3-acetic acid (IAA) is the predominant auxin in nature. Auxin regulates cell expansion and cell division in a dose dependent way. Therefore, plants evolved an extremely complex yet highly coordinated network to maintain auxin homeostasis, including IAA biosynthesis, transport, conjugation and oxidation. Among these, the least known process is IAA oxidation. Discovering how IAA is terminated is very important in completing the whole picture of IAA homeostatic regulation. By partial purification of IAA oxidases from Arabidopsis, we detected IAA oxidation activity from both microsomal fractions and soluble fractions. We first investigated the protein in microsomal fraction and identified one oxidase named as ACC oxidase 2 (ACO2), an ethylene synthetase that belongs to 2-oxoglutarate and iron (II) [2OG(Fe)] dependent dioxygenase family. In vitro enzyme assays with IAA showed that ACO2 could catabolize IAA and that the product had the same retention time as indole-3-carbinal (ICA), an decarboxylative IAA oxidation product. The same enzyme assay with the ACO2 homologues ACO3 was conducted, and ACO3 showed similar activity. An ACO2 loss-of-function allele showed ethylene related phenotypes, including longer hypocotyls and reduced apical hook angle in etiolated seedlings, and delayed bolting. Further, null aco2 mutants also showed reduced phototropic bending, a typical auxin related phenotype. These results indicate that ACO2 might be involved in both ethylene and auxin signaling. We also investigated the soluble IAA oxidases, AtDAO1 (DAO1) and AtDAO2 (DAO2). In vitro enzyme assays showed that both recombinant DAO1 and DAO2 have IAA oxidation activity and the product is the non-decarboxylated 2-oxindole-3-acetic acid (oxIAA), the major IAA metabolite observed under normal growth conditions. Analysis of the loss-of-function null allele dao1-1 showed that DAO1 is the predominant IAA oxidase and is responsible for 95% of oxIAA production in Arabidopsis seedlings. Dysregulation of IAA oxidation altered the IAA metabolism profile and causes accumulation of other IAA conjugates and a series of morphological alteration, including elongation of organs, increased lateral roots and delayed sepal opening. Investigation of expression patterns shows that DAO1 is a cytosolic protein that widely expressed throughout the plant, especially in the root tip, the pericycle of root, the cotyledon, and the sepal, highly correlating to the phenotypes of dao1-1. These results suggest that IAA oxidation plays an important role in IAA homeostasis during the whole life of Arabidopsis.