SAGA1 and SAGA2 localize the starch sheath to the pyrenoid in Chlamydomonas reinhardtii.
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The purified SAGA2 tandem CBM20 construct (both native CBM20 domains) binds starch granules; the mVenus control does not
"We observed that both the 10×His-mVenus-2×SAGA1-CBM20 and the 10×His-mVenus-SAGA2-2×CBM20 proteins, but not a 10×His-mVenus control protein, bound to starch"
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The construct contains both native SAGA2 CBM20 domains
"SAGA2 natively has two consecutive CBM20 domains, both of which were included in the SAGA2 construct for this experiment"
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beta-cyclodextrin and maltoheptaose compete with starch binding
"Binding of 10×His-mVenus-2×SAGA1-CBM20 and the 10×His-mVenus-SAGA2-2×CBM20 to starch was decreased in the presence of either β-cyclodextrin or maltoheptaose, suggesting that each protein bound to all three molecules."
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SAGA2 is depleted from starch-tubule-matrix junctions, where SAGA1 is enriched
"Our results indicate that whereas SAGA1 is enriched at the starch–tubule–matrix junctions of the pyrenoid, SAGA2 is depleted from these regions"
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saga2 has reduced matrix starch coverage early in pyrenoid formation, rescued by SAGA2-Venus
"Taken together, these results indicate that SAGA2 is necessary for normal matrix–starch sheath coverage early during pyrenoid formation."
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The saga2 sheath defect recovers at later stages
"other factors can compensate for a lack of SAGA2 to assemble an apparently normal starch sheath during later stages of pyrenoid formation"
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saga2 grows normally at limiting CO2
"SAGA2 is not necessary for growth under limiting CO2 conditions"
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SAGA2 is not needed for a single pyrenoid or for tubules
"These observations indicate that SAGA2 is not necessary for pyrenoid tubule formation."
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The saga1;saga2 double mutant lacks starch sheaths
"Remarkably, at both time points, the saga1;saga2 mutant completely lacked starch sheaths and had almost no starch associated with its visible pyrenoid condensates"
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SAGA1 and SAGA2 act redundantly to localize the starch sheath
"suggesting that SAGA1 and SAGA2 function redundantly to localize starch sheaths to the pyrenoid"
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In the double mutant starch lies throughout the stroma
"We conclude that in the saga1;saga2 double mutant, starch is distributed throughout the stroma rather than to the pyrenoid matrix condensates."