Premium
Target of rapamycin‐signaling modulates starch accumulation via glycogenin phosphorylation status in the unicellular red alga Cyanidioschyzon merolae
Author(s) -
Pancha Imran,
Shima Hiroki,
Higashitani Nahoko,
Igarashi Kazuhiko,
Higashitani Atsushi,
Tanaka Kan,
Imamura Sousuke
Publication year - 2019
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1111/tpj.14136
Subject(s) - phosphorylation , transcriptome , biochemistry , starch , biology , glycogen , microbiology and biotechnology , chemistry , gene , gene expression
SUMMARY The target of rapamycin ( TOR ) signaling pathway is involved in starch accumulation in various eukaryotic organisms; however, the molecular mechanism behind this phenomenon in eukaryotes has not been elucidated. We report a regulatory mechanism of starch accumulation by TOR in the unicellular red alga, Cyanidioschyzon merolae . The starch content in C. merolae after TOR ‐inactivation by rapamycin, a TOR ‐specific inhibitor, was increased by approximately 10‐fold in comparison with its drug vehicle, dimethyl sulfoxide. However, our previous transcriptome analysis showed that the expression level of genes related to carbohydrate metabolism was unaffected by rapamycin, indicating that starch accumulation is regulated at post‐transcriptional levels. In this study, we performed a phosphoproteome analysis using liquid chromatography‐tandem mass spectrometry to investigate potential post‐transcriptional modifications, and identified 52 proteins as candidate TOR substrates. Among the possible substrates, we focused on the function of Cm GLG 1, because its phosphorylation at the Ser613 residue was decreased after rapamycin treatment, and overexpression of Cm GLG 1 resulted in a 4.7‐fold higher starch content. Cm GLG 1 is similar to the priming protein, glycogenin, which is required for the initiation of starch/glycogen synthesis, and a budding yeast complementation assay demonstrated that Cm GLG 1 can functionally substitute for glycogenin. We found an approximately 60% reduction in the starch content in a phospho‐mimicking Cm GLG 1 overexpression strain, in which Ser613 was substituted with aspartic acid, in comparison with the wild‐type Cm GLG 1 overexpression cells. Our results indicate that TOR modulates starch accumulation by changing the phosphorylation status of the Cm GLG 1 Ser613 residue in C. merolae .