Abstract
Enhancing the photosynthetic induction response to fluctuating light has been suggested as a key target for improvement in crop breeding programmes, with the potential to substantially increase whole-canopy carbon assimilation and contribute to crop yield potential. Rubisco activation may be the main physiological process that will allow us to achieve such a goal. In this study, we assessed the phenotype of Rubisco activation rate in a doubled haploid (DH) barley mapping population [131 lines from a Yerong/Franklin (Y/F) cross] after a switch from moderate to saturating light. Rates of Rubisco activation were found to be highly variable across the mapping population, with a median activation rate of 0.1 min−1 in the slowest genotype and 0.74 min−1 in the fastest genotype. A unique quantitative trait locus (QTL) for Rubisco activation rate was identified on chromosome 7H. This is the first report on the identification of a QTL for Rubisco activation rate in planta and the discovery opens the door to marker-assisted breeding to improve whole-canopy photosynthesis of barley. This also suggests that genetic factors other than the previously characterized Rubisco activase (RCA) isoforms on chromosome 4H control Rubisco activity. Further strength is given to this finding as this QTL co-localized with QTLs identified for steady-state photosynthesis and stomatal conductance. Several other distinct QTLs were identified for these steady-state traits, with a common overlapping QTL on chromosome 2H, and distinct QTLs for photosynthesis and stomatal conductance identified on chromosomes 4H and 5H, respectively. Future work should aim to validate these QTLs under field conditions so that they can be used to aid plant breeding efforts.
Highlights
By 2050, the global population is expected to rise to 9 billion and to meet future food demand we will need to increase crop production worldwide by 70 % (Paul et al 2019)
Future work should aim to validate these quantitative trait locus (QTL) under field conditions so that they can be used to aid plant breeding efforts
Q1/τ.sun-7H was flanked by the bpb-9601 DArT marker which has previously been associated with both grain yield and crop spike number in the Y/F population (Xue et al 2010). This marker is of particular interest as it flanks QTLs that we identified for steady-state A and gs (QA.sun-7H and Qgs.sun-7H in Table 1), highlighting its utility for marker-assisted selection (MAS)
Summary
By 2050, the global population is expected to rise to 9 billion and to meet future food demand we will need to increase crop production worldwide by 70 % (Paul et al 2019). Improving the photosynthetic efficiency of crop species has been shown to boost plant growth under field conditions (Kromdijk et al 2016; South et al 2019). Received: 9 August 2020; Editorial decision: 6 November 2020; Accepted: 18 November 2020 The light environment of the lower canopy is subject to continuous and dynamic change across the course of a day, caused by movement of the sun across the sky, sporadic cloud cover and/or movement of upper elements in the canopy caused by wind (Slattery et al 2018) These processes can cause a leaf in low/moderate light one moment to suddenly be exposed to saturating light conditions the next. Stomatal responses to fluctuating light are considered to be a much more challenging target for improvement than the biochemical limitations to photosynthesis (for a comprehensive review of limitations to dynamic photosynthesis, see Kaiser et al 2019)
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