Investigating auxin import and export proteins in Chlorella vulgaris

SUMMARY Chlorella vulgaris is a unicellular freshwater green alga that has promising applications in biofuel and food production. Current research on C. vulgaris focuses on cell wall degradation methods to extract nutrients, but research into other areas of C. vulgaris can improve current methods of resource production. One clear candidate for further study is auxin, a plant hormone that stimulates cell division and macromolecule accumulation in C. vulgaris; auxin secretion has also been implicated in cell communication in other species of algae. Unfortunately, C. vulgaris’ response to auxin is not well studied, and it is unknown if C. vulgaris even secretes auxin. To shed light on these unknowns, we hypothesized that C. vulgaris possesses membrane-bound auxin transport proteins. We tested this hypothesis by treating C. vulgaris with cellulase to create protoplasts, cells without cell walls, and observing whether they swelled in response to auxin. Provisional evidence for swelling helped set up further experiments assaying C. vulgaris cultures for auxin secretion. Protoplasts were treated with supernatant extracted from centrifuged cell culture and then observed for swelling. The results of the experiment showed significant increases in protoplast size, indicating auxin presence in the supernatant, and suggest that C. vulgaris is capable of secreting auxin. In addition, the rapid swelling of protoplasts suggests the presence of auxin import proteins and alternate auxin signaling pathways. These results contribute to a better understanding of auxin transport and response in C. vulgaris, which have implications for more efficient growth and resource extraction of C. vulgaris.