Photorespiration differs among Arabidopsis thaliana ecotypes and is correlated with photosynthesis.

Nicholas J Tomeo,David M Rosenthal

doi:10.1093/jxb/ery274

Abstract

A greater understanding of natural variation in photosynthesis will inform strategies for crop improvement by revealing overlooked opportunities. We use Arabidopsis thaliana ecotypes as a model system to assess (i) how photosynthesis and photorespiration covary and (ii) how mesophyll conductance influences water use efficiency (WUE). Phenotypic variation in photorespiratory CO2 efflux was correlated with assimilation rates and two metrics of photosynthetic capacity (i.e. VCmax and Jmax); however, genetic correlations were not detected between photosynthesis and photorespiration. We found standing genetic variation-as broad-sense heritability-for most photosynthetic traits, including photorespiration. Genetic correlation between photosynthetic electron transport and carboxylation capacities indicates that these traits are genetically constrained. Winter ecotypes had greater mesophyll conductance, maximum carboxylation capacity, maximum electron transport capacity, and leaf structural robustness when compared with spring ecotypes. Stomatal conductance varied little in winter ecotypes, leading to a positive correlation between integrated WUE and mesophyll conductance. Thus, variation in mesophyll conductance can modulate WUE among A. thaliana ecotypes without a significant loss in assimilation. Genetic correlations between traits supplying energy and carbon to the Calvin-Benson cycle are consistent with biochemical models, suggesting that selection on either of these traits would improve all of them. Similarly, the lack of a genetic correlation between photosynthesis and photorespiration suggests that the positive scaling of these two traits can be broken.

Highlights

Despite a near complete description of the photorespiratory pathway, availability and characterization of knockout mutants for many of the enzymes in the pathway (Maurino and Peterhansel, 2010), and thorough understanding of the response of photorespiration to environmental stimuli, relatively little is known about natural genetic variation in photorespiration (Nunes-Nesi et al, 2016)
Phenotypic variation in photorespiratory CO2 efflux was correlated with assimilation rates and two metrics of photosynthetic capacity (i.e. VCmax and Jmax); genetic correlations were not detected between photosynthesis and photorespiration
We found a strong co-ordination between assimilation and photorespiration as we show that photorespiration was phenotypically correlated with net carbon assimilation (AN), and with the maximum capacities for carboxylation and electron transport (i.e. VCmax and J850; Fig. 3)

Summary

Introduction

Despite a near complete description of the photorespiratory pathway, availability and characterization of knockout mutants for many of the enzymes in the pathway (Maurino and Peterhansel, 2010), and thorough understanding of the response of photorespiration to environmental stimuli, relatively little is known about natural genetic variation in photorespiration (Nunes-Nesi et al, 2016). Photorespiration occurs when 2-phosphoglycolate is formed by the oxygenation of ribulose-1,5-bisphosphate (RuBP) by Rubisco.Briefly,two 2-phosphoglycolate molecules are metabolized via the C2 photorespiratory pathway, resulting in the return of one phosphoglycerate to the Calvin–Benson cycle, and the release of one CO2 molecule, and consumption of. Natural genetic variation has provided many yield-enhancing traits including pathogen and pest resistance (Foster et al, 1991; Hill et al, 2006), improved heat tolerance (Maestri et al, 2002), yield enhancement through increasing harvest indices (Hay, 1995), and the proliferation of dwarfing genes in cereals (Hedden, 2003), to name a few

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