Hybrid Cyanobacterial-Tobacco Rubisco Supports Autotrophic Growth and Procarboxysomal Aggregation.

Douglas J Orr,Maureen R Hanson,Dawn Worrall,Elizabete Carmo-Silva,Myat T Lin,Martin A J Parry

doi:10.1104/pp.19.01193

Douglas J Orr, Maureen R Hanson + Show 4 more

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https://doi.org/10.1104/pp.19.01193

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Journal: Plant Physiology	Publication Date: Nov 19, 2019
Citations: 23	License type: CC BY 4.0

Affiliation: Lancaster University, Cornell University

Abstract

Much of the research aimed at improving photosynthesis and crop productivity attempts to overcome shortcomings of the primary CO2-fixing enzyme Rubisco. Cyanobacteria utilize a CO2-concentrating mechanism (CCM), which encapsulates Rubisco with poor specificity but a relatively fast catalytic rate within a carboxysome microcompartment. Alongside the active transport of bicarbonate into the cell and localization of carbonic anhydrase within the carboxysome shell with Rubisco, cyanobacteria are able to overcome the limitations of Rubisco via localization within a high-CO2 environment. As part of ongoing efforts to engineer a β-cyanobacterial CCM into land plants, we investigated the potential for Rubisco large subunits (LSU) from the β-cyanobacterium Synechococcus elongatus (Se) to form aggregated Rubisco complexes with the carboxysome linker protein CcmM35 within tobacco (Nicotiana tabacum) chloroplasts. Transplastomic plants were produced that lacked cognate Se Rubisco small subunits (SSU) and expressed the Se LSU in place of tobacco LSU, with and without CcmM35. Plants were able to form a hybrid enzyme utilizing tobacco SSU and the Se LSU, allowing slow autotrophic growth in high CO2 CcmM35 was able to form large Rubisco aggregates with the Se LSU, and these incorporated small amounts of native tobacco SSU. Plants lacking the Se SSU showed delayed growth, poor photosynthetic capacity, and significantly reduced Rubisco activity compared with both wild-type tobacco and lines expressing the Se SSU. These results demonstrate the ability of the Se LSU and CcmM35 to form large aggregates without the cognate Se SSU in planta, harboring active Rubisco that enables plant growth, albeit at a much slower pace than plants expressing the cognate Se SSU.

Highlights

The need to produce sufficient food for a growing population requires increasing the productivity and efficiency of agriculture in order to increase yields by the estimated 70% that will be needed by 2050(Lobell et al, 2009; Ray et al, 2012)
As part of ongoing efforts to engineer a β‐cyanobacterial concentrating mechanism (CCM) into land plants, we investigated the potential for Rubisco large subunits (LSU) from the β‐cyanobacteria Synechococcus elongatus (Se) to form aggregated
The current study describes two new transplastomic tobacco lines, namely SeL and SeLM35, where the native Rubisco large subunit gene (rbcL) gene has been replaced with its cyanobacterial counterpart without the Se‐rbcS gene

Summary

Introduction

The need to produce sufficient food for a growing population requires increasing the productivity and efficiency of agriculture in order to increase yields by the estimated 70% that will be needed by 2050(Lobell et al, 2009; Ray et al, 2012). Given its central role in crop growth and productivity, improving photosynthesis is one approach that has the potential to generate step‐change improvements in crop yields and resource use efficiency (Long et al, 2006; Ort et al, 2015). At current atmospheric levels of CO2 and O2, Rubisco’s tendency to oxygenate rather than carboxylate its substrate ribulose 1,5‐bisphosphate (RuBP) is estimated to reduce yields by as much as 36% and 20% in US grown soybean (Glycine max) and wheat (Triticum aestivum), respectively (Walker et al, 2016). One example is the introduction of CO2‐concentrating mechanisms (CCMs) into C3 crops to increase CO2 concentrations at the site of Rubisco, a strategy which is likely to dramatically reduce the propensity of Rubisco to carry out oxygenation reactions by creating an environment which favors the beneficial carboxylation reaction (Price et al, 2011; McGrath and Long, 2014; Hanson et al, 2016; Long et al., 2016). Significant research efforts are being invested in this area, with varying sources for the CCMs being engineered, such as C4 (Hibberd et al, 2008; Langdale, 2011) and crassulacean acid metabolism (CAM) (Borland et al, 2014; Yang et al, 2015) systems from plants, and the pyrenoid and carboxysome‐

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