Localization and structure of plastidial-encoded polymerase sub-units

Abstract

Chloroplast biogenesis is a quintessential process In plants for the acquisition of photo-autotrophy. The path towards chloroplast biogenesis begins with the inhibition of skotomorphogenesis (That is the growth program in the dark), followed by photomorphogenesis through phytochrome-mediated red light sensing leading to the initiation of chloroplast biogenesis. We have observed that plants do not develop properly and show an albino phenotype when PAPs are lacking, indicating that chloroplast biogenesis does not occur. Previous experiments have shown that a complex dubbed Plastid Encoded Polymerase (PEP) interacting with Polymerase Associated Proteins (PAP) is the major player in setting a functional chloroplast. Given the semi-autonomous nature of the chloroplast genome, it is established that a cross-talk must occur with the nuclear genome. The white (albino) phenotype is observed with the genetic excision of any single PAP, indicating that the whole complex is no longer able to form or function. Interestingly both a chloroplastic-transit peptide and a nuclear localization signal have been predicted within the sequences of six PAP proteins. To validate these predictions and gain insight on the role of selected PAP proteins, I have chosen to pursue the subcellular localization and protein-protein interactions of these essential proteins. Moreover structural characterization will help us understand the function of each of these proteins within the PEP/PAP complex.