Heterologous expression of chromo- and fluorescent proteins in the green algae Chlamydomonas reinhardtii to evaluate their impact on photosynthesis and growth rates.

Melany Villegas

Fluorescent proteins (FPs) are used as in vivo molecular markers, in addition, close relatives from corals include the chromoproteins (CPs), which exhibit distinctive visible colours but not fluorescence. Here, we engineered a group of eight CPs and five FPs to express from the nuclear genome and localize in the chloroplast of the microalga Chlamydomonas reinhardtii to determine their effects on algal photosynthesisDifferences in photosynthetic parameters as the maximum quantum efficiency of photosystem II (Fv/Fm), the relative electron transport rate (rETR), and growth of the transformants compared to the parental strain were investigated. Across all strains, consistent Fv/Fm values (∼ 0.77) were observed, indicating functional photosynthetic machinery. Higher rETR values were observed in CP expressing transformants under higher light intensities (131, 267, 420, and 597 μmol m-2 s-1) compared to parental and FP strains, suggesting the CPs promote more efficient electron transport at higher light intensities. These findings were specific to transformants confirmed to express certain CPs to high levels by Western blot and were mirrored by stable performance on plate growth assays in high light. Although further investigation is needed to confirm these findings, CPs may be further exploited to enhance growth of engineered algae in extreme light conditions.


Keywords: Chromoproteins, Fluorescent proteins, reef organisms, Chlamydomonas reinhardtii, chlorophyll a fluorescence, photoprotection.