Characterization and Transformation of reg Cluster Genes in Volvox powersii Enable Investigation of Convergent Evolution of Cellular Differentiation in Volvox

• Published in: Protist 2021-10, Vol.172 (5-6), p.125834-125834, Article 125834
• Main Authors: Grochau-Wright, Zachariah I., Ferris, Patrick J., Tumberger, John, Jiménez-Marin, Berenice, Olson, Bradley J.S.C., Michod, Richard E.
• Format: Article
• Language: English
• Subjects: Base Sequence; Cell Differentiation; Chlorophyta; genetic transformation; germ-soma differentiation; multicellularity; reg cluster; VARL genes; Volvocine algae; Volvox - genetics
• ISSN: 1434-4610; 1618-0941
• DOI: 10.1016/j.protis.2021.125834

•Volvox is a model system for the evolution of cellular differentiation.•Volvox powersii has an ancestral developmental program versus other Volvox species.•A developmental mutant of V. powersii contains a mutation in its rlsB gene.•Transformation of mutant with WT rlsB does not result in phenotypic rescue.•We show reg cluster sequence data and first genetic transformation of V. powersii. The evolution of germ-soma cellular differentiation represents a key step in the evolution of multicellular individuality. Volvox carteri and its relatives, the volvocine green algae, provide a model system for studying the evolution of cellular differentiation. In V. carteri, the regA gene controls somatic cell differentiation and is found in a group of paralogs called the reg cluster, along with rlsA, rlsB, and rlsC. However, the developmental program of V. carteri is derived compared to other volvocine algae. Here we examine Volvox powersii which possesses an ancestral developmental program and independent evolution of the Volvox body plan. We sequenced the reg cluster from V. powersii wild-type and a mutant with fewer cells and altered germ-soma ratio. We found that the mutant strain’s rlsB gene has a deletion predicted to cause a truncated protein product. We developed a genetic transformation procedure to insert wild-type rlsB into the mutant strain. Transformation did not result in phenotypic rescue, suggesting the rlsB mutation is insufficient for generating the mutant phenotype. The transformation techniques and sequences described here provide essential tools to study V. powersii, a species well suited for studying the evolution of cellular differentiation and convergent evolution of Volvox morphology.