While the biochemistry of how the starch polymers are made is relatively well understood, very little is known about how the formation of a starch granule initiates within the plastid.
Also, factors controlling the number of starch granules initiated per plastid are poorly understood.
We were involved in the discovery and characterisation of several novel proteins that are required for proper granule initiation – including the Protein Targeting to Starch (PTST) family proteins.
We are focusing on investigating starch granule initiation in the wheat endosperm.
During grain development, there are two temporally separated waves of granule initiation that give rise to large A-type granules and small B-type granules.
We have made the important discovery that A- and B-type granule initiations occur through distinct biochemical mechanisms; and have elucidated multiple factors required for the proper timing and number of granule initiations during grain development.
We are currently using both genetic and biochemical approaches to elucidate how all these components work together.
Figure 1: Our molecular model of how starch granules initiate during wheat grain development. SS4 and BGC1 promote the initiation of large A-type granules within amyloplasts during early grain development. In later stages of grain development, PHS1 and BGC1 promote the formation of small B-type granules. The electron micrographs on the right show that the phs1 mutant (which lacks PHS1) has substantially fewer small B-type granules than the wild type (WT). Figure adapted from Kamble et al. (2023) Plant Cell. https://doi.org/10.1093/plcell/koad217