Enhancing starch levels, granule size and phosphate content in Chlamydomonas reinhardtii through overexpression of ChlreSEX4

Abstract

Chlamydomonas reinhardtii is a green alga that has been widely used as a model organism for studying various cellular processes, including starch metabolism. In this alga, starch undergoes continuous phosphorylation during its synthesis and degradation. We recently identified and characterized ChlreSEX4 (starch excess 4), a glucan phosphatase from C. reinhardtii, orthologous to Arabidopsis thaliana SEX4, which is able to bind and dephosphorylate amylopectin in vitro. To explore the possibility of manipulating starch phosphorylation levels in C. reinhardtii, we overexpressed the ChlreSEX4 gene in Chlamydomonas and characterized the resulting lines. Results showed a high phosphatase activity in the overexpressing lines, accompanied by an increase in starch content, greater granule size and higher levels of granule-bound phosphate, without changes in triglyceride content. This work allowed us not only to discover a new method to enhance starch accumulation without affecting the lipid content of the alga, but also to obtain a more phosphorylated starch, which would have diverseapplications in biotechnology.