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

Abstract

In order to investigate starch accumulation, and the enzymes activity changes and the expression levels of genes and their relationships among them at different developmental stages of wheat grain. We choose Annong9912 and E28 were used in the study. During starch accumulating rate and grain filling rate, and there were obvious genotype difference between Annong9912 and E28. Whether low or high starch content of starch content, the accumulation courses of amylopectin, amylose and total starch were well fitted to the logistic equation by relating starch contents against DAP. The simulation parameters revealed that the higher contents of amylopectin and amylose resulted from earlier initiating accumulation time and greater accumulation rate. And amylose, amylopectin and total starch accumulation rate of two wheat cultures were significantly and positively correlated with activities of SBE, SSS and GBSS, but amylose accumulation rate of E28 had no correlation with the activities of SBE. In addition, there were significant correlations among activities of SBE, SSS and GBSS in two wheat cultivars. We speculated that these enzymes proteins may have a coordinating action in starch biosynthesis within the amyloplast, operating as functional multiprotein complexes. And expression levels of enzyme genes demonstrated a single-peak curve, and 12-18 DAP reached their peaks and then began to drop, and all had high expression level in earlier stage of endosperm development, but in E28 were higher than in Annong9912. The GBSS-I transcripts on average were expressed over 60 times more than GBSS-II transcript in E28. SBE, SSS, DBE may control starch synthesis at the transcriptional level, and GBSS-I may control starch synthesis at the post transcriptional level. The expression level of DBE on average was lower than SS-1 and SBE-IIa genes, and similar to SS-III and SBE-IIb genes, but higher than GBSS-I and GBSS-II genes.

Keywords: Enzyme activity; Gene expression; RT-PCR; Starch; Starch synthase.

Fig. 1

Changes in starch content and starch accumulating rate during pollination (n = 9). A ₁ amylopse contents A ₂ amylopse accumulating rate B ₁ amylopectin contents B ₂ amylopectin accumulating rate C ₁ total contents C ₂ total content accumulating rate

Fig. 2

Changes in enzyme activities of SSS, GBSS, SBE and DBE during pollination (n = 9). A SSS enzyme activity B GBSS enzyme activity C SBE enzyme activity D DBE enzyme activity. SSS soluble starch synthase; GBSS granules bound starch synthase; SBE starch branching enzyme; DBE debranching enzyme

Fig. 3

Changes in enzyme genes relative expression during pollination (n = 9). A GBSS-I enzyme gene B GBSS-II enzyme gene C SS-I enzyme gene D SS-II enzyme gene E SSS-III enzyme gene F SBE-IIa enzyme gene G SBE-IIb enzyme gene H SBE-I enzyme gene I DBE enzyme gene. SS starch synthase; GBSS granules bound starch synthase; SBE starch branching enzyme; DBE debranching enzyme