Browsing by Author "Zhu, Ling"
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Item Light regulation and functional characterization of Phytochrome Interacting Factor 1 (PIF1) in Arabidopsis(2012-05) Zhu, Ling; Huq, Enamul; Jansen, Robert; Lloyd, Alan; O'Halloran, Theresa; Roux, StanleyPlants sense light intensity, quality and direction through a group of photoreceptors to modulate their growth and development. One family of photoreceptor is called phytochromes (phys) that perceives red and far red light. Phys transduce light signals via a sub-family of the basic Helix-Loop-Helix (bHLH) transcription factors called Phytochrome Interacting Factors (PIFs). PIFs function as negative regulators in the phy-mediated light signaling pathways. In darkness, PIFs regulate downstream gene expressions to inhibit photomorphogenesis. Upon light exposure, PIFs are phosphorylated and poly-ubiquitylated prior to their rapid degradation through the 26S proteasome pathway. One of the PIFs, PIF1, has the highest affinity for both phyA and phyB and also displayed the fastest degradation kinetics under both red and far red light. Here we showed that PIF1 directly and indirectly regulates key genes involved in chlorophyll biosynthesis to optimize the greening process in Arabidopsis. PIF1 binds to a G-box (CACGTG) DNA sequence element present in its direct target genes (e.g., protochlorophyllide oxidoreductase C, PORC) in darkness and regulates their expression. Structure-function studies revealed two separate regions called APB and APA necessary for binding to phyB and phyA, respectively, located at the amino-terminus and a novel phosphorylation site at the carboxy-terminus of PIF1. Both amino- and carboxy-terminal regions are necessary for the light-induced degradation of PIF1. However, the DNA binding is not necessary for the light-induced degradation of PIF1. Using a targeted systems biology approach, we identified new factors, HECATE proteins that promote photomorphogenesis by negatively regulating the function of PIF1. Moreover, we employed an unbiased genetic screening using luciferase imaging system to identify new mutants defective in the light-induced degradation of PIF1. The cloning and characterization of these mutants will help identify the factors, such as the kinase and E3 ligase, responsible for the light-induced degradation of PIF1. Taken together, these data revealed detail mechanisms of how PIF1 negatively regulates photomorphogenesis and how light induces rapid degradation of PIF1 to promote photomorphogenesis.Item Manage the Margins: Three Essays on Effective Policymaking for Social Inequality in Health(2011-10-21) Zhu, LingThis dissertation includes three studies, devoted to trying to understand inequality in health between people from different social groups in a democratic society. In the U.S., social inequality in health takes various forms and the key to understanding how democracy solves the problem of inequality lies in a complex set of political and social factors. I take an institutional approach and focus on examining how political and policy institutions, their administrative processes, and the policy implementation environment are linked to social inequality in health. The first essay, Whose Baby Matters More, uses a theoretical framework for evaluating heterogeneous group responses to public health policies and depicts how racial disparities in health are rooted in group heterogeneity in policy responses. The second essay, Anxious Girls and Inactive Boys, focuses on how state-level policy interventions and social capital interactively affect gender differences in health. The third essay, Responsibility for Equity, explores the link between publicness of state healthcare systems and social equity in healthcare access. In the first essay, I focus on racial disparities in infant mortality rates and pool state-level data from 1990 to 2006. The empirical analysis suggests that enhancing the capacity of state healthcare systems is critical to improving population health. Blacks and whites, nevertheless, exhibit different responses to the same policy. Racial disparities could be reduced only when policy interventions generate more relative benefits for Blacks. In the second essay, I find that social capital conditions the effect of public health policies with regard to managing childhood obesity. There are gender differences, moreover, in health outcomes and behavioral responses to state and local-level obesity policies. In the third essay, I find that different institutional factors exhibit different impact on inequality in healthcare access. While public finance resources may reduce inequality in healthcare access, public ownership and the public healthcare workforce do not have significant association with inequality in healthcare access. State Medicaid eligibility rules exhibit moderate impact on inequality in healthcare access.