TY  - JOUR
A1  - Merida, Angel
A1  - Fettke, Jörg
T1  - Starch granule initiation in Arabidopsis thaliana chloroplasts
JF  - The plant journal
N2  - The initiation of starch granule formation and the mechanism controlling the number of granules per plastid have been some of the most elusive aspects of starch metabolism. This review covers the advances made in the study of these processes. The analyses presented herein depict a scenario in which starch synthase isoform 4 (SS4) provides the elongating activity necessary for the initiation of starch granule formation. However, this protein does not act alone; other polypeptides are required for the initiation of an appropriate number of starch granules per chloroplast. The functions of this group of polypeptides include providing suitable substrates (maltooligosaccharides) to SS4, the localization of the starch initiation machinery to the thylakoid membranes, and facilitating the correct folding of SS4. The number of starch granules per chloroplast is tightly regulated and depends on the developmental stage of the leaves and their metabolic status. Plastidial phosphorylase (PHS1) and other enzymes play an essential role in this process since they are necessary for the synthesis of the substrates used by the initiation machinery. The mechanism of starch granule formation initiation in Arabidopsis seems to be generalizable to other plants and also to the synthesis of long-term storage starch. The latter, however, shows specific features due to the presence of more isoforms, the absence of constantly recurring starch synthesis and degradation, and the metabolic characteristics of the storage sink organs.
KW  - starch granules
KW  - starch metabolism
KW  - starch granule initiation
KW  - starch
KW  - granule number per chloroplast
KW  - starch morphology
KW  - Arabidopsis thaliana
Y1  - 2021
U6  - https://doi.org/10.1111/tpj.15359
SN  - 0960-7412
SN  - 1365-313X
VL  - 107
IS  - 3
SP  - 688
EP  - 697
PB  - Wiley
CY  - Hoboken
ER  -