The physiological and epigenetic effects of dynamic light acclimation in Arabidopsis thaliana

The majority of the world’s crops are grown outdoors, covering 1.6 billion hectares of land, where they are subjected to dynamic light conditions. Plant light acclimation has been extensively studied, but lesser understanding on physiological processes from the impact of dynamic light fluctuations. Understanding the impact of fluctuating light on photosynthesis, and how plants acclimate is key for improving plant light responses and could allow identification of novel targets for crop improvements. Previous work demonstrated that naturally fluctuating regimes reduced photosynthetic efficiency and increased net CO2 assimilation in Arabidopsis thaliana. Utilising these same regimes, results were replicated to demonstrate phenotypic consistency. This was key to investigating epigenetic change where a consistent phenotype indicated consistent epigenetic change. Assessment of differential methylation between square and fluctuating light regimes, more typical in field environments, demonstrated widespread changes in DNA methylation, with a subset of these methylated regions also relating to changes in transcription. The oxidation and reduction state have a role in regulating photosynthesis. To further understand this regulation under fluctuating light cp12-1/2/3 knockdown/knockout lines were grown under differing light regimes and the reduced expression of CP12 assessed. The physiological assessment of these plants showed reduction in CP12 expression which negatively impacted fluctuating light acclimation, with reductions in assimilation rates and increased non-photochemical quenching. These findings illustrate that naturally fluctuating light has multiple consequences for plants which can be regulated by DNA methylation. Importantly, it further demonstrates that square light regimes are not reflective of field environments, with changes in DNA methylation and expression providing some explanation to these mechanisms. Furthermore, it suggests the need to consider how plants are grown, particularly if translating results into agricultural settings. Finally, this work provides a suite of genes which could be targeted to improve responses to fluctuating light, potentially improving crop yields.