Reference "Identification of the ADP-glucose pyrophosphorylase isoforms essential for starch synthesis in the leaf and seed endosperm of rice (Oryza sativa L.)"

Reference ID

11555

Title

Identification of the ADP-glucose pyrophosphorylase isoforms essential for starch synthesis in the leaf and seed endosperm of rice (Oryza sativa L.)

Source

Plant molecular biology, 2007, vol. , pp. -

Authors (13)

Lee-S-K	Hwang-S-K	Han-M	Eom-J-S
Kang-H-G	Han-Y	Choi-S-B	Cho-M-H
Bhoo-S-H	An-G	Hahn-T-R	Okita-T-W
Jeon-J-S

Abstract

ADP-glucose pyrophosphorylase (AGP) catalyzes the first committed step of starch
biosynthesis in higher plants. To identify AGP isoforms essential for this
biosynthetic process in sink and source tissues of rice plants, we analyzed the
rice AGP gene family which consists of two genes, OsAGPS1 and OsAGPS2, encoding
small subunits (SSU) and four genes, OsAGPL1, OsAGPL2, OsAGPL3 and OsAGPL4,
encoding large subunits (LSU) of this enzyme heterotetrameric complex.
Subcellular localization studies using green fluorescent protein (GFP) fusion
constructs indicate that OsAGPS2a, the product of the leaf-preferential
transcript of OsAGPS2, and OsAGPS1, OsAGPL1, OsAGPL3, and OsAGPL4 are plastid-
targeted isoforms. In contrast, two isoforms, SSU OsAGPS2b which is a product of
a seed-specific transcript of OsAGPS2, and LSU OsAGPL2, are localized in the
cytosol. Analysis of osagps2 and osagpl2 mutants revealed that a lesion of one
of the two cytosolic isoforms, OsAGPL2 and OsAGPS2b, causes a shrunken endosperm
due to a remarkable reduction in starch synthesis. In leaves, however, only the
osagps2 mutant appears to severely reduce the transitory starch content.
Interestingly, the osagps2 mutant was indistinguishable from wild type during
vegetative plant growth. Western blot analysis of the osagp mutants and wild
type plants demonstrated that OsAGPS2a is an SSU isoform mainly present in
leaves, and that OsAGPS2b and OsAGPL2 are the major SSU and LSU isoforms,
respectively, in the endosperm. Finally, we propose a spatiotemporal complex
model of OsAGP SSU and LSU isoforms in leaves and in developing endosperm of
rice plants.