Plastid terminal oxidase requires translocation to the grana stacks to act as a sink for electron transport

Abstract

Abstract:The plastid terminal oxidase (PTOX) has been shown to be an important sink for photosynthetic electron transport in stress tolerant plants. However, overexpression studies in stress sensitive species have previously failed to induce significant activity of this protein.Here we show that overexpression of PTOX from the salt tolerant brassica species Eutrema salsugineum does not, alone, result in activity, but that over-expressing plants show faster induction and a greater final level of PTOX activity once exposed to salt stress. This implies that an additional activation step is required before activity is induced. We show that that activation involves the translocation of the protein from the unstacked stromal lamellae to the thylakoid grana and a protection of the protein from trypsin digestion. This represents an important and novel activation step and opens up new possibilities in the search for stress tolerant crops. Significance statement:Growing concerns about food security and changing climates make the identification of novel stress tolerance traits a priority. Here we show that the activation of the plastid terminal oxidase, via its relocation within the thylakoid membrane, can induce a protective sink for electron transport. We have thus identified a novel and unexpected mechanism for protein activation and opened new avenues for engineering plant stress tolerance.3 /body

Mutation of the Atypical Kinase ABC1K3 Partially Rescues the PROTON GRADIENT REGULATION 6 Phenotype in Arabidopsis thaliana

“…This leads to the conclusion that the photoactive PQ pool size per se has a limited influence on photosynthetic efficiency, and that the photosynthetic defect becomes symptomatic only when PQ limitation is associated with an additional impairment in its mobility. Impaired PQ mobility may be the cause affecting the reoxidation of the photoactive PQ by PTOX, since it may require an exchange between grana stacks and stroma lamellae ( Figure 6A; Stepien and Johnson, 2018). Furthermore, it would affect the exchange between the photoactive pool and the reservoir stored in the PGs necessary to maintain the photoactive PQ pool size (Pralon et al, 2019).…”

How do vascular plants perform photosynthesis in extreme environments? An integrative ecophysiological and biochemical story

“…In agreement with these findings, a recent study has shown the crucial role of PTOX in enabling growth under intermittent light conditions (Nawrocki et al , ). In model species, PTOX must be transferred to the grana to develop its photoprotective role (Stepien and Johnson, ). A recent study of plants originating from the Gurbantünggüt Temperate Desert (north‐west China) revealed an increased PQ pool oxidation and enhanced PSI activity when grown under high light, in comparison with Arabidopsis thaliana (Tu et al , ).…”

Chlororespiration Controls Growth Under Intermittent Light

“…The low rate of electron flow sustained by PTOX ranges from 0.1 to 5 e 2 PSII 21 s 21 in the chloroplasts of plants and C. reinhardtii (Houille-Vernes et al, 2011;Trouillard et al, 2012), which does not qualify PTOX as an efficient electron sink. Despite its low reaction rate, PTOX has been suggested to play a photoprotective role when the light absorption by PSII exceeds the capacity of the downstream reactions (Carol et al, 1999;Niyogi, 2000;Ort and Baker, 2002;Krieger-Liszkay and Feilke, 2016;Stepien and Johnson, 2018). We first examined the participation of PTOX in a pathway that reroutes electrons from PSII by monitoring the electron transfer rate (ETR PSII ) in the wild type and the ptox2 mutant over a wide range of light intensities.…”