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STARCH SYNTHASE 4 is required for normal starch granule initiation in amyloplasts of wheat endosperm
Author(s) -
Hawkins Erica,
Chen Jiawen,
WatsonLazowski Alexander,
AhnJarvis Jennifer,
Barclay J. Elaine,
Fahy Brendan,
Hartley Matthew,
Warren Frederick J.,
Seung David
Publication year - 2021
Publication title -
new phytologist
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.742
H-Index - 244
eISSN - 1469-8137
pISSN - 0028-646X
DOI - 10.1111/nph.17342
Subject(s) - amyloplast , endosperm , granule (geology) , starch , starch synthase , biology , mutant , botany , biochemistry , plastid , chloroplast , amylose , gene , amylopectin , paleontology
Summary Starch granule initiation is poorly understood at the molecular level. The glucosyltransferase, STARCH SYNTHASE 4 (SS4), plays a central role in granule initiation in Arabidopsis leaves, but its function in cereal endosperms is unknown. We investigated the role of SS4 in wheat, which has a distinct spatiotemporal pattern of granule initiation during grain development. We generated TILLING mutants in tetraploid wheat ( Triticum turgidum ) that are defective in both SS4 homoeologs. The morphology of endosperm starch was examined in developing and mature grains. SS4 deficiency led to severe alterations in endosperm starch granule morphology. During early grain development, while the wild‐type initiated single ‘A‐type’ granules per amyloplast, most amyloplasts in the mutant formed compound granules due to multiple initiations. This phenotype was similar to mutants deficient in B‐GRANULE CONTENT 1 (BGC1). SS4 deficiency also reduced starch content in leaves and pollen grains. We propose that SS4 and BGC1 are required for the proper control of granule initiation during early grain development that leads to a single A‐type granule per amyloplast. The absence of either protein results in a variable number of initiations per amyloplast and compound granule formation.