Role of hybrid cluster protein 4 in anaerobic metabolism in Chlamydomonas reinhardtii

Abstract

The unicellular green algae Chlamydomonas reinhardtii (C. reinhardtii) has long been studied for its unique fermentation pathways and is recently being considered as a candidate organism in biofuel production. Fermentation in C. reinhardtii is facilitated by a network of three predominant pathways producing four major by products: formate, ethanol, acetate and hydrogen. Recent microarray studies have identified many previously unknown genes highly up-regulated during anaerobiosis, and new tools for the targeted gene disruption make reverse genetics possible in C. reinhardtii for the first time. For example, hybrid cluster protein 4 (HCP4) is one of the most highly up-regulated genes during anaerobiosis in C. reinhardtii, displaying a nearly 1,600 fold increase upon anoxia. Hybrid cluster proteins have long been studied for their unique spectroscopic properties, yet their biological functions remain unclear. In this study HCP4 was knocked down using artificial microRNAs, followed by extensive phenotypic analyses. This study shows that knockdown of HCP4 affects the regulation of many key fermentative genes as well as metabolic flux and nitrogen uptake.