Evaluating light use efficiency of different C4 subtypes in C3 background

Background

C4 crops, such as maize and sorghum, often yield more than C3 crops per unit land because of the higher energy conversion efficiency of C4 crops. Introducing the C4 pathway into rice is widely considered as a necessary strategy, to ultimately improve agricultural productivity. Evaluating different C4 CO2 concentrating mechanisms in C3 background is, therefore, critical for the application of C4 components to improve C3 photosynthesis. 

Project description

The C3 crop rice, one of the major food crops, needs to increase its production by 50% by 2050. C4 crops yield more than C3 crops because of their higher photosynthetic rates, due to the operation of a CO2 concentrating mechanism (CCM) that ensures a high CO2 concentration around Rubisco, thus minimizing RuBP oxygenation and photorespiratory loss.

Introducing the C4 pathway into rice is required to improve its yields. The CCM requires ATP to operate, and the CCM cycle in current crop-C4 type (like maize) accounts for >40% of the total ATP required for CO2 assimilation; in contrast, the non-domesticated, PEP-CK C4 type theoretically requires much less ATP and therefore is preferred to achieve high rice yields. However, the observed light-use efficiency is not higher in PEP-CK than in crop-C4 plants. This is probably because there is more CO2 leakage in PEP-CK than in crop-C4 plants as a result of differences in underlying biochemistry and associated Kranz anatomical leaf structures.

To overcome this potential confounding effect of higher leakage, I aim to introduce different C4 pathways of biochemistry (including crop-C4 and PEP-CK types) into mesophyll cells of rice and evaluate the engineered single-cell C4 systems by comparing their phenotypes for light-use efficiency and other physiological characteristics.  

Research objectives 

The main aim of this project is to evaluate the model prediction (Yin & Struik, 2021) of ɸCO2 and yielding potential of C4 pathways applied in C3 rice. It will be achieved by introducing different single-cell C4 pathways into C3 rice and then examining the engineered C4 systems via comparing their phenotypes and physiological characteristics related to photosynthetic light- use efficiency. 

The specific objectives are: 

• to construct different single-cell C4 types in the same C3 background;
• to evaluate the effects of CO2 leakiness from different subcellular position on the same single-cell PEP-CK type;
• to assess the potential of engineering for the PEP-CK type in lowering ATP cost and increasing photosynthetic rate.

Methods 

This project will generate rice materials of two different single-cell C4 types using multi-gene transformation method. The materials will be evaluated in terms of their light-use efficiencies.