The Role of Chloroplast Localized Molecular Chaperone HSP90 in Arabidopsis thaliana Development

Heat shock protein 90 (HSP90) is a molecular chaperone and it has been implicated in late stages of de novo protein folding. In Arabidopsis thaliana, there are seven HSP90 isoforms. In this project, the function of chloroplast-localized AtHSP90.5 was studied by analyzing transgenic plants overexpressing AtHSP90.5FLAG. In addition, three independent transgenic lines showing AtHSP90.5 co-suppression were identified to have an albino phenotype in photosynthetic tissues along with stunted plant growth, reduced vegetative leaf size, and malformation of thylakoid membranes. Furthermore, potential AtHSP90.5 co-chaperones and client proteins were screened via yeast two-hybrid and affinity purification coupled with mass spectrometry, and nine potential AtHSP90.5 interactors were obtained. A novel client protein of AtHSP90.5, PsbO1 (Oxygen-evolving enhancer protein 1), was identified by yeast two-hybrid. The interaction between HSP90.5 and PsbO1 was further investigated and a putative role of AtHSP90.5 in promoting PsbO1 folding and targeting to thylakoid lumen is proposed.MAS