Analysis of a Bifunctional Plastid Nucleoid Protein: Ferrodoxin-Sulfite Reductase

University Of Southern Mississippi, Hattiesburg MS

Investigators

Abstract

The importance of chloroplast-encoded genes for plant growth and productivity is unquestionable, yet surprisingly, many aspects of molecular biology and biochemistry of the organelle, such as the control of chloroplast development and intracellular communication of signals related to this process are only poorly understood. The sequencing of several higher plant plastomes has provided valuable information of types and number of genes that are encoded by ctDNA and has greatly increased our knowledge of organellar gene regulation on the transcriptional and translational level. On the other hand, higher-level structural determinants that very likely have profound effects on the expression of plastome-encoded genes are essentially unknown. Since the plastome is associated with proteins that condense the multiple genome copies into compact complexes termed nucleoids, rearrangements of nucleoids must occur to allow transcription, replication, recombination and repair to take place. While nucleoid protein composition is known to change with plastid development, the molecular details of these remodeling events and the way(s) in which they affect the fundamental aspects of plastid nucleic acid metabolism are unknown. This project addresses the molecular basis of nucleoid structure and function by studying expression and regulation of interaction with DNA of a major structural protein of plastid nucleoids. Through a combined genetic, biochemical and cell biological approach, the biological significance of the association of DCP68/SiR with the plastid nucleoid will be assessed. DCP68/SiR appears to be a bifunctional plastid protein that fulfills dual roles in the organelle as a nucleoid constituent and an enzyme of the sulfate reduction pathway that leads to the biosynthesis of cysteine and other sulfur-containing metabolites. Because of the intriguing possibility that regulation of nucleoid structure and function is connected with that of the assimilatory sulfur metabolism, the results from this study will contribute to an understanding of the molecular processes and regulatory strategies in the plant cell that govern organellar development and function. The study will begin to elucidate the contribution of nucleoid structure in regulating plastid gene expression and plastome transmission and maintenance, and will thereby aid future efforts to develop efficient plastome genetic manipulation strategies. The photosynthetic organelles (chloroplasts) of plant cells contain their own genetic material (DNA) that encodes many products of great importance for plant growth and productivity. Chloroplast DNA is bound to proteins that condense it into so-called nucleoids whose structure and, presumably, function, change during plant growth and development. This project addresses the effects chloroplast DNA-compacting proteins have on the ability of the organelle's DNA to provide a template for duplication and for information retrieval. The study focuses on the chloroplast nucleoid protein DCP68, which condenses DNA and plays the additional role in the chloroplast of converting sulfur minerals to a form that is usable by the plant. The study will examine how environmental and internal signals affect the interaction between DCP68 and chloroplast DNA and might connect nucleoid structure and function with other metabolic aspects of the organelle.