Intersystem photosynthetic redox signal in retrograde chloroplast-to-nucleus communication

To analyze the impact of photosynthetic redox signals, light sources with spectral qualities that preferentially excite either Photosystem I (PSI light) or Photosystem II (PSII light) were used. The light sources have been described in (Wagner et al, Planta 2008). Strong reduction signals were induced by light shifts from PSI to PSII light (PSI-II). In order to find primary regulated genes the acclimation responses were monitored at 30 min and 60 min after a light shift. The control was continuous Psi light at the same time. We used stn7 (a thylakoid redox regulated kinase) to specifically block transduction of photosynthetic redox signal in order to compare “real” redox regulated with that of other light acclimation pathways. Keywords: photosynthesis, redox regulation, light acclimation, retrograde signalling, long term response Experiments were performed with plant material corresponding to pools of at least 250 individuals of Arabidopsis thaliana (Col-0 and stn7; SALK_073254 in Col-0 background). To abtain healthy and unstressed plants, seedlings were initially grown for 20 days under continuous white light on soil. Plants were then pre-acclimated to PSI-light for 3 days. Plants were then shifted to PSII light and tissue was harvested at the described time points. As control we utilized the stn7 knockout mutant which does not perceive PQ- related photosynthetic redox signals. RNA isolation: Leaf material was harvested and frozen in liquid N2 under the respective light source. Isolation of total RNA was performed as adapted from Logemann et al Analytical Biochemistry, 1987.