Overexpression of the Rieske FeS protein of the Cytochrome b6f complex increases C4 photosynthesis in Setaria viridis

Maria Ermakova,Maria Ermakova,Patricia E Lopez-Calcagno,Christine A Raines,Susanne Von Caemmerer,Susanne Von Caemmerer,Robert T Furbank,Robert T Furbank

doi:10.1038/s42003-019-0561-9

Maria Ermakova, Maria Ermakova + Show 6 more

Open Access

https://doi.org/10.1038/s42003-019-0561-9

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Abstract

C4 photosynthesis is characterised by a CO2 concentrating mechanism that operates between mesophyll and bundle sheath cells increasing CO2 partial pressure at the site of Rubisco and photosynthetic efficiency. Electron transport chains in both cell types supply ATP and NADPH for C4 photosynthesis. Cytochrome b6f is a key control point of electron transport in C3 plants. To study whether C4 photosynthesis is limited by electron transport we constitutively overexpressed the Rieske FeS subunit in Setaria viridis. This resulted in a higher Cytochrome b6f content in mesophyll and bundle sheath cells without marked changes in the abundances of other photosynthetic proteins. Rieske overexpression plants showed better light conversion efficiency in both Photosystems and could generate higher proton-motive force across the thylakoid membrane underpinning an increase in CO2 assimilation rate at ambient and saturating CO2 and high light. Our results demonstrate that removing electron transport limitations can increase C4 photosynthesis.

Highlights

C4 photosynthesis is characterised by a CO2 concentrating mechanism that operates between mesophyll and bundle sheath cells increasing CO2 partial pressure at the site of ribulose bisphosphate carboxylase oxygenase (Rubisco) and photosynthetic efficiency
Eleven T0 transgenic plants were selected on the basis of hygromicin resistance and a subset of nine lines was analysed for Rieske FeS protein abundance, the presence of the BdPetC transcript and insertion numbers (Fig. 1a)
Rieske FeS and Rubisco large subunit protein abundances per leaf area were highly variable between transgenic and control plants in the T0 generation (Fig. 1a), because T0 plants have been regenerated from the tissue culture at different times and varied substantially in age

Summary

Introduction

C4 photosynthesis is characterised by a CO2 concentrating mechanism that operates between mesophyll and bundle sheath cells increasing CO2 partial pressure at the site of Rubisco and photosynthetic efficiency. To study whether C4 photosynthesis is limited by electron transport we constitutively overexpressed the Rieske FeS subunit in Setaria viridis This resulted in a higher Cytochrome b6f content in mesophyll and bundle sheath cells without marked changes in the abundances of other photosynthetic proteins. ATP and NADPH essential for CO2 assimilation and are a target for improvement[4] It has been demonstrated in C3 plants that facilitating electron transport by overexpressing the components of electron transfer chain can result in higher assimilation rates[5,6]. In C3 plants the electron transport chain is localised to the thylakoid membranes of mesophyll cells and consists of four major protein complexes: Photosystem II (PSII), Cytochrome b6f (cytb6f), Photosystem I (PSI) and ATP synthase.

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