Expression profiling of genes involved in starch synthesis in sink and source organs of rice

Abstract

A comprehensive analysis of the transcript levels of genes which encode starch-synthesis enzymes is fundamental for the assessment of the function of each enzyme and the regulatory mechanism for starch biosynthesis in source and sink organs. Using quantitative real-time RT-PCR, an examination was made of the expression profiles of 27 rice genes encoding six classes of enzymes, i.e. ADPglucose pyrophosphorylase (AGPase), starch synthase, starch branching enzyme, starch debranching enzyme, starch phosphorylase, and disproportionating enzyme in developing seeds and leaves. The modes of gene expression were tissue- and developmental stage-specific. Four patterns of expression in the seed were identified: group 1 genes, which are expressed very early in grain formation and are presumed to be involved in the construction of fundamental cell machineries, de novo synthesis of glucan primers, and initiation of starch granules; group 2 genes, which are highly expressed throughout endosperm development; group 3 genes, which have transcripts that are low at the onset but which rise steeply at the start of starch synthesis in the endosperm and are thought to play essential roles in endosperm starch synthesis; and group 4 genes, which are expressed scantly, mainly at the onset of grain development, and might be involved in synthesis of starch in the pericarp. The methodology also revealed that the defect in the cytosolic AGPase small subunit2b (AGPS2b) transcription from the AGPS2 gene in endosperm sharply enhanced the expressions of endosperm and leaf plastidial AGPS1, the endosperm cytosolic AGPase large subunit2 (AGPL2), and the leaf plastidial AGPL1.

Starch accumulation, activities of key enzyme and gene expression in starch synthesis of wheat endosperm with different starch contents

“…Nevertheless, it should be kept in mind that the transcript levels are not always related to their enzymatic activities or protein levels, considering post-transcriptional and posttranslational controls (Sun et al 2005). There are intricate functional interactions between components of the starch biosynthetic system during wheat endosperm, and the starch-biosynthesizing system in higher plants demands the concerted expression of many genes at any particular developmental stage of a particular tissue (Tetlow et al 2004;Ohdan et al 2005;Hennen-Bierwagen et al 2008). In addition to maintaining the activity levels of individual enzymes, several combinations of protein-protein interactions, such as those among the wheat proteins for SBEI, SBEIIb, and DBE might play an essential role in the metabolic regulation of starch biosynthesis.…”

Spatiotemporal Profiling of Starch Biosynthesis and Degradation in the Developing Barley Grain

“…The AGP-S1b and AGP-S2 translation products are predicted to be plastid targeted, while the AGP-S1a subunit was shown to be cytosolic (Rösti et al, 2006). Only two AGP-L cDNAs, AGP-L1 and AGP-L2, were identified, despite evidence for four genes in the rice genome (Ohdan et al, 2005). Both gene products are predicted as plastid localized.…”

Gradually Decreasing Starch Branching Enzyme Expression Is Responsible for the Formation of Heterogeneous Starch Granules

“…One microgram of total RNA was reverse transcribed. The primers and detailed procedures used in the analysis were derived from the methods of Ohdan et al (2005).…”