Consequences of light spectra for pigment composition and gene expression in the cryptophyte Rhodomonas salina

Algae with a more diverse suite of pigments can, in principle, exploit a broader swath of the light spectrum through chromatic acclimation, the ability to maximize light capture via plasticity of pigment composition. We grew Rhodomonas salina in wide‐spectrum, red, green, and blue environments and measured how pigment composition differed. We also measured expression of key light‐capture and photosynthesis‐related genes and performed a transcriptome‐wide expression analysis. We observed the highest concentration of phycoerythrin in green light, consistent with chromatic acclimation. Other pigments showed trends inconsistent with chromatic acclimation, possibly due to feedback loops among pigments or high‐energy light acclimation. Expression of some photosynthesis‐related genes was sensitive to spectrum, although expression of most was not. The phycoerythrin α‐subunit was expressed two‐orders of magnitude greater than the β‐subunit even though the peptides are needed in an equimolar ratio. Expression of genes related to chlorophyll‐binding and phycoerythrin concentration were correlated, indicating a potential synthesis relationship. Pigment concentrations and expression of related genes were generally uncorrelated, implying post‐transcriptional regulation of pigments. Overall, most differentially expressed genes were not related to photosynthesis; thus, examining associations between light spectrum and other organismal functions, including sexual reproduction and glycolysis, may be important. Algal responses to changes in light spectrum are more complex than predicted by the theory of chromatic acclimation. Chromatic acclimation may be regulated post‐transcriptionally, and other physiological processes may be linked to changes in light spectrum.