Improving C₃ photosynthesis by exploiting natural genetic variation: Hirschfeldia incana as a model species

Despite research efforts toward improving crop photosynthetic energy conversion efficiencies over the past 40 years, photosynthetic efficiencies remain far from their theoretical maxima. A major challenge has been that plant photosynthesis is a complex process, controlled by many underlying genetic factors and highly dynamic in response to short-term environmental changes. Recent approaches to improving photosynthesis involved model-based identification of the bottlenecks in photosynthesis followed by their genetic modification (GM). While these approaches were successful and inspirational, their dependency on the use of GM techniques may restrict their implementation in some jurisdictions. We therefore suggest greater research focus on a different, yet complementary, approach to improving photosynthetic efficiency: the exploration and exploitation of natural genetic variation in photosynthesis. A substantial improvement in phenotyping and genotyping technology over the past decade has highlighted natural variation in photosynthetic sub-traits for crop and model species. However, a comprehensive understanding of all the factors responsible for photosynthetic limitations is still lacking. We therefore propose the use of high photosynthetic capacity species as models for the exploration of the physiological and genetic basis of high photosynthetic efficiency. While most high photosynthetic capacity species are not suitable as models due to complex genetics and evolutionary distance from crops, we have identified Brassicaceae species Hirschfeldia incana (L.) Lagr.-Foss as a promising candidate. In this perspective paper, we describe and advocate the use of H. incana as a model for the exploration of high maximum CO₂ assimilation rates (P_max) found in some C₃ species. We describe the basic biology and evolutionary history of the species and report preliminary data on its photosynthetic characteristics. Our findings suggest H. incana is an excellent model species for studies aiming at understanding natural genetic variation in photosynthetic efficiency.