STARCH SYNTHASE 4 is required for normal starch granule initiation in amyloplasts of wheat endosperm

Starch granule initiation is poorly understood at the molecular level. The glucosyltransferase, STARCH SYNTHASE 4 (SS4), plays a central role in Arabidopsis leaves, but its function cereal endosperms unknown. We investigated of SS4 wheat, which has distinct spatiotemporal pattern during grain development. generated TILLING mutants tetraploid wheat (Triticum turgidum) that are defective both homoeologs. morphology endosperm starch was examined developing and mature grains. deficiency led to severe alterations morphology. During early development, while wild-type initiated single ‘A-type’ granules per amyloplast, most amyloplasts mutant formed compound due multiple initiations. This phenotype similar deficient B-GRANULE CONTENT 1 (BGC1). also reduced content leaves pollen propose BGC1 required for proper control development leads A-type amyloplast. absence either protein results variable number initiations amyloplast formation.