AUTHOR=Koo Kwang M. , Jung Sera , Lee Beom S. , Kim Jin-Baek , Jo Yeong D. , Choi Hong-Il , Kang Si-Yong , Chung Gook-H. , Jeong Won-Joong , Ahn Joon-Woo 

TITLE=The Mechanism of Starch Over-Accumulation in Chlamydomonas reinhardtii High-Starch Mutants Identified by Comparative Transcriptome Analysis

JOURNAL=Frontiers in Microbiology

VOLUME=8

YEAR=2017

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2017.00858

DOI=10.3389/fmicb.2017.00858

ISSN=1664-302X

ABSTRACT=<p>The focus of this study was the mechanism of starch accumulation in <italic>Chlamydomonas reinhardtii</italic> high-starch mutants. Three <italic>C</italic>. <italic>reinhardtii</italic> mutants showing high-starch content were generated using gamma irradiation. When grown under nitrogen-deficient conditions, these mutants had more than twice as much starch than a wild-type control. The mechanism of starch over-accumulation in these mutants was studied with comparative transcriptome analysis. In all mutants, induction of <italic>phosphoglucomutase 1</italic> (<italic>PGM1</italic>) expression was detected; PGM1 catalyzes the inter-conversion of glucose 1-phosphate and glucose 6-phosphate in both starch biosynthetic and glycolytic pathway. Interestingly, transcript levels of <italic>phosphoglucose isomerase 1</italic> (<italic>PGI1</italic>), <italic>fructose 1,6-bisphosphate aldolase 1</italic> and <italic>2</italic> (<italic>FBA1</italic> and <italic>FBA2</italic>) were down-regulated in all mutants; PGI1, FBA1, and FBA2 act on downstream of glucose 6-phosphate conversion in glycolytic pathway. Therefore, down-regulations of <italic>PGI1, FBA1</italic>, and <italic>FBA2</italic> may lead to accumulation of upstream metabolites, notably glucose 6-phosphate, resulting in induction of <italic>PGM1</italic> expression through feed-forward regulation and that <italic>PGM1</italic> overexpression caused starch over-accumulation in mutants. These results suggest that PGI1, FBA1, FBA2, and PGM1 correlate with each other in terms of coordinated transcriptional regulation and play central roles for starch over-accumulation in <italic>C</italic>. <italic>reinhardtii</italic>.</p>