Browsing by Subject "Flowering"
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Item Comparative Genomics of Gossypium spp. through GBS and Candidate Genes ? Delving into the Controlling Factors behind Photoperiodic Flowering(2013-08-09) Young, Carla Jo LoganCotton has been a world-wide economic staple in textiles and oil production. There has been a concerted effort for cotton improvement to increase yield and quality to compete with non-natural man-made fibers. Unfortunately, cultivated cotton has limited genetic diversity; therefore finding new marketable traits within cultivated cotton has reached a plateau. To alleviate this problem, traditional breeding programs have been attempting to incorporate practical traits from wild relatives into cultivated lines. This incorporation has presented a new problem: uncultivated cotton hampered by photoperiodism. Traditionally, due to differing floral times, wild and cultivated cotton species were unable to be bred together in many commercial production areas world-wide. This worldwide breeding problem has inhibited new trait incorporation. Before favorable traits from undomesticated cotton could be integrated into cultivated elite lines using marker-assisted selection breeding, the markers associated with photoperiod independence needed to be discovered. In order to increase information about this debilitating trait, we set out to identify informative markers associated with photoperiodism. This study was segmented into four areas. First, we reviewed the history of cotton to highlight current problems in production. Next, we explored cotton?s floral development through a study of floral transition candidate genes. The third area was an in-depth analysis of Phytochrome C (previously linked to photoperiod independence in other crops). In the final area of study, we used Genotype-By-Sequencing (GBS), in a segregating population, was used to determine photoperiod independence associated with single nucleotide polymorphisms (SNPs). In short, this research reported SNP differences in thirty-eight candidate gene homologs within the flowering time network, including photoreceptors, light dependent transcripts, circadian clock regulators, and floral integrators. Also, our research linked other discrete SNP differences, in addition to those contained within candidate genes, to photoperiodicity within cotton. In conclusion, the SNP markers that our study found may be used in future marker assisted selection (MAS) breeding schemas to incorporate desirable traits into elite lines without the introgression of photoperiod sensitivity.Item Mechanisms underlying vernalization-mediated VERNALIZATION INSENSITIVE 3 (VIN3) induction in Arabidopsis thaliana(2013-05) Zografos, Brett Robert; Sung, SibumVernalization is defined as the response to prolonged cold exposure required for acquiring the molecular competence necessary to undergo floral transition. FLOWERING LOCUS C (FLC), a potent floral repressor in Arabidopsis, is highly expressed before vernalizing cold treatment but is repressed during prolonged vernalization. VERNALIZATION INSENSITIVE 3 (VIN3) is a Plant HomeoDomein (PHD)- containing protein that is required for establishing vernalization-mediated repression of FLC. The induction of VIN3 is one of the earliest molecular events in vernalization response and its expression is intimately linked to prolonged cold exposure. However, mechanisms underlying VIN3 induction remain poorly understood. The constitutive repression of VIN3 in the absence of cold is due to multiple repressive components, including a transposable element-derived sequence, LIKE-HETEROCHROMA TIN PROTEIN 1 (LHP1), and POLYCOMB REPRESSION COMPLEX 2 (PRC2). Furthermore, the full extent of VIN3 induction by vernalization requires activating complex components, including EARLY FLOWERING 7 (ELF7) and EARLY FLOWERING IN SHORT DAYS (EFS). Dynamic changes in the histone modifications present at VIN3 chromatin during vernalization were also observed, indicating that chromatin changes play a critical role in regulating VIN3 induction. However, VIN3 induction by vernalization still occurs in the absence of activation complexes and de- repression of VIN3 in the absence of the repressive complexes is not sufficient for achieving complete induction. Thus, unknown cold-influenced regulators responsible for achieving maximum VIN3 induction during vernalization must exist. Therefore, forward genetic screening was undertaken to elucidate upstream regulators of VIN3. Molecular characterization of T-DNA mutant populations elucidated two interesting mutants: a mutant that ectopically expressed VIN3 before cold (ectopic VIN3 induction, evi1) and mutants that failed to induce VIN3 during vernalization (defects in VIN3 induction, dvi1). FLC is over-expressed in dvi1 despite its failure to induce VIN3 expression during vernalization, suggesting that this mutant may regulate both VIN3 and FLC. In evi1, FLC is hyper-repressed after 40 days of vernalization, leading to an acceleration of flowering time. These results indicate that regulators of VIN3 in the vernalization pathway exist and that these regulators may use different mechanisms in order to influence VIN3 expression.Item Sorghum Ma5 and Ma6 maturity genes(2009-05-15) Brady, Jeffrey AlanThe Ma5 and Ma6 maturity loci in sorghum contain genes interacting epistatically to block flowering until an appropriate daylength is met. Because sorghum is a crop of tropical origin, its critical daylength is close to 12 hours. Sorghums with dominant alleles at these two loci are photoperiod sensitive, extremely late flowering, and ill-suited to cultivation in the temperate U.S. Most sorghum lines grown in the U.S. have been converted to photoperiod insensitive plants that have recessive mutations at the ma6 locus. This work describes ongoing efforts to clone the genes responsible for the Ma5/Ma6 ? controlled late flowering response in sorghum. To reach this goal, the two loci were mapped with AFLP and SSR markers that were part of an integrated genetic, physical, and cytogenetic map of the sorghum genome. Genetic markers have been linked to both the Ma5 and Ma6 loci on chromosomes 2 and 6, respectively. BAC libraries have been screened to identify numerous BACs associated with each locus. Additional work to fine-map each locus and identify potential candidate genes by comparison with the rice genome is ongoing.