Calcium-dependent regulation of photosynthesis in Chlamydomonas reinhardtii: Structural and functional dynamics of calredoxin, a chloroplast Ca2+-dependent thioredoxin

• Applicant: Professor Dr. Michael Hippler
• Subject Area: Plant Biochemistry and Biophysics
• Term: from 2012 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 224873199

Chloroplast Ca2+-transport (import/export), allocation, sensing and/or signaling appear to be essential for chloroplast biology and in particular for effective photosynthesis in green algae and vascular plants. There is evidence that a regulatory network exists which senses the chloroplast Ca2+ content, participates in regulation of photosynthesis and control of protein expression. Yet, basic aspects of this network are unknown. Herein we will focus on calredoxin (CRX), a newly identified factor in this network, which operates as a Ca2+-dependent thioredoxin (TRX) in the chloroplast. As a Ca2+-dependent sensor-responder, CRX links calcium and redox responses. Ca2+-binding to CRX remodels its structure allowing binding and electron transfer to chloroplast peroxiredoxin (PRX1), important for photo-acclimation responses. It is our aim (i) to mechanistically understand protein-protein interaction between CRX and PRX1. Here, the goal is to comprehend how the Ca2+-driven structural changes permit binding and electron transfer between CRX and PRX1. We further aim (ii) for dissecting the interconnection of CRX in the Ca2+- and redox-dependent regulatory networks and to understand its impact on chloroplast redox poise and photo-protection. Moreover, we aim (iii) to identify factors that control expression of CRX and thereby possibly expand the link between photoreception and photosynthesis as well as between calcium and redox control in chloroplasts.

• DFG Programme: Research Grants