Natural genetic variation for acclimation of photosynthetic light use efficiency to growth irradiance in Arabidopsis

Plants are known to be able to acclimate their photosynthesis to the level of irradiance. Here we present the analysis of natural genetic variation for photosynthetic light use efficiency (FPSII) in response to five light environments among 12 genetically diverse Arabidopsis thaliana accessions. We measured acclimation of FPSII to constant growth irradiances of four different levels (100, 200, 400, and 600 µmol m-2 s-1) by imaging chlorophyll fluorescence after 24 days of growth, and compared these results to acclimation of FPSII to a step-wise change in irradiance where the growth irradiance was increased from 100 to 600 µmol m-2 s-1 after 24 days of growth. Genotypic variation for FPSII is shown by calculating heritability for short-term FPSII response to different irradiance levels, as well as for the relation of FPSII measured at light saturation (a measure of photosynthetic capacity) to growth irradiance level, and for the kinetics of the response to a step-wise increase in irradiance from 100 to 600 µmol m-2 s-1. A genome-wide association study for FPSII measured one hour after a step-wise increase in irradiance identified several new candidate genes controlling this trait. In conclusion, the different photosynthetic responses to a changing light environment displayed by different Arabidopsis are due to genetic differences and we have identified candidate genes for the photosynthetic response to an irradiance change. The genetic variation for photosynthetic acclimation to irradiance found in this study will allow future identification and analysis of the causal genes for the regulation of FPSII in plant