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 (ΦPSII) in response to five light environments among 12 genetically diverse Arabidopsis (Arabidopsis thaliana) accessions. We measured the acclimation of ΦPSIIto constant growth irradiances of four different levels (100, 200, 400, and 600μmolm⁻²⁻¹) by imaging chlorophyll fluorescence after 24 d of growth and compared these results with acclimation of ΦPSIIto a step-wise change in irradiance where the growth irradiance was increased from 100 to 600μmol⁻²⁻¹ after 24 d of growth. Genotypic variation for ΦPSIIis shown by calculating heritability for the short-term ΦPSIIresponse to different irradiance levels as well as for the relation of ΦPSIImeasured 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 600μmol ⁻²⁻¹. A genome-wide association study for ΦPSIImeasured 1 h 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 accessions 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 genesfor the regulation of ΦPSIIin plants.