Enhanced photosynthetic efficiency for increased carbon assimilation and woody biomass production in hybrid poplar INRA 717-1B4

Abstract

Increasing CO2 levels in the atmosphere and the resulting negative impacts on climate change have compelled global efforts to achieve carbon neutrality or negativity. Most such efforts focus on carbon sequestration through chemical or physical approaches. We aim to harness the power of synthetic biology to enhance plants natural ability to draw down and sequester carbon, thereby positively affecting climate change. Past decades of scientific progress have shed light on strategies to overcome the intrinsic limitations of carbon drawdown and fixation through photosynthesis, particularly in row crops in hopes of improving agricultural productivity for food security. Incorporating a photorespiration bypass in C3 plants has shown promising results of increased biomass and grain yield. Despite their globally dominant role in atmospheric carbon flux, the drawdown rates of most trees are currently limited by their C3 photosynthetic metabolism, and efforts to improve the photosynthetic capacity of trees, such as by reducing energy loss in photorespiration, are currently lacking. Here, we selected a photorespiration bypass pathway and tested its effectiveness on photosynthetic enhancement in hybrid poplar INRA717-IB4. The design includes a RNAi strategy to reduce the transportation of the photorespiration byproduct, glycolate, out of chloroplast and a shunt pathway to metabolize the retained glycolate back to CO2 for fixation through the Calvin-Benson cycle. Molecular and physiological data collected from two repeated growth experiments indicates that transgenic plants expressing genes in the photorespiration bypass pathway have increased photosynthetic efficiency, leading to faster plant growth and elevated biomass production. One lead transgenic event accumulated 53% more above-ground dry biomass over a five month growth period in a controlled environment. Pilot projects with photosynthesis-enhanced trees in the field are in progress. Our results provide a proof-of-concept for engineering trees to help combat climate change.

Advancing chloroplast synthetic biology through high-throughput plastome engineering ofChlamydomonas reinhardtii

“…These two enzymes cause the direct decarboxylation of the photorespiration product glycolate into CO 2 , which increases CO 2 concentrations in the chloroplast and was reported to improve photosynthetic yield in different crops. 7,68…”

“…These two enzymes cause the direct decarboxylation of the photorespiration product glycolate into CO2, which increases CO2 concentrations in the chloroplast and was reported to improve photosynthetic yield in different crops. 7,68 As host for our engineering efforts, we chose a CO2-concentrating mechanism deficient-and glycolate dehydrogenase-deficient C. reinhardtii mutant (cc-5797, genotype confirmation in Supplementary Fig. 2c-d) that shows a severe growth phenotype under atmospheric CO2 concentrations due to increased photorespiration 69 .…”

Why cutting respiratory CO2 loss from crops is possible, practicable, and prudential

“…Increasing photosynthetic CO 2 fixation has been the dominant metabolic paradigm for increasing crop yields for >40 years, [1][2][3][4] and has now also become a dominant paradigm for plant-based carbon sequestration strategies. 5,6 The alternative of reducing respiratory CO 2 production has-like plant respiration in general (Figure 1a) 7 -had far less research even though plants release roughly half the carbon fixed by photosynthesis back to the atmosphere via respiration (Figure 1b). 8,9 Plant respiration (often called 'dark' respiration) refers to the CO 2 released when photosynthate, typically taken as hexose, is metabolised to provide carbon skeletons, ATP and reducing power for various processes.…”

“…Increasing photosynthetic CO 2 fixation has been the dominant metabolic paradigm for increasing crop yields for >40 years, 1–4 and has now also become a dominant paradigm for plant‐based carbon sequestration strategies 5,6 . The alternative of reducing respiratory CO 2 production has—like plant respiration in general (Figure 1a) 7 —had far less research even though plants release roughly half the carbon fixed by photosynthesis back to the atmosphere via respiration (Figure 1b).…”