Differential Pattern of Expression and Sugar Regulation of Arabidopsis thaliana ADP-glucose Pyrophosphorylase-encoding Genes

Abstract

ADP-glucose pyrophoshorylase (ADP-Glc PPase) catalyzes the first and limiting step in starch biosynthesis. In plants, the enzyme is composed of two types of subunits (small and large) and is allosterically regulated by 3-phosphoglycerate and phosphate. The pattern of expression and sugar regulation of the six Arabidopsis thaliana ADP-Glc PPase-encoding genes (two small subunits, ApS1 and ApS2; and four large subunits, ApL1-ApL4) has been studied. Based on mRNA expression, ApS1 is the main small subunit or catalytic isoform responsible for ADP-Glc PPase activity in all tissues of the plant. Large subunits play a regulatory role, and the data presented define a clear functional distinction among them. ApL1 is the main large subunit in source tissues, whereas ApL3 and, to a lesser extent, ApL4 are the main isoforms present in sink tissues. Thus, in source tissues, ADP-Glc PPase would be finely regulated by the 3-phosphoglycerate/phosphate ratio, whereas in sink tissues, the enzyme would be dependent on the availability of substrates for starch synthesis. Sugar regulation of ADP-Glc PPase genes is restricted to ApL3 and ApL4 in leaves. Sugar induction of ApL3 and ApL4 transcription in leaves allows the establishment of heterotetramers less sensitive to the allosteric effectors, resembling the situation in sink tissues. The results presented on the expression pattern and sugar regulation allow us to propose a gene evolution model for the Arabidopsis ADP-Glc PPase gene family.

Activation of ADP-Glucose Pyrophosphorylase Gene Promoters by a WRKY Transcription Factor, AtWRKY20,in Arabidopsis thalianaL. and Sweet Potato (Ipomoea batatasLam.)

“…However, ApS1 showed a sucrose-insensitive expression pattern under normal physiological conditions when mature A. thaliana plants were irrigated with sucrose-containing Murashige and Skoog medium, whereas ApL3 was induced by irrigation with the sucrose-containing medium (Crevillén et al, 2005). These observations suggest that the sucrosemediated regulation mechanism for the expression of the small subunit gene may be different from that for the large subunit gene.…”

“…Each subunit is encoded by a different gene. Six genes encode proteins with homology to AGPase in the Arabidopsis thaliana genome (Crevillén et al, 2005). Two of these genes encode small subunits, ApS1 (locus number At5g48300) and ApS2 (locus number At1g05610), and the other four encode large subunits, ApL1 to ApL4 (locus numbers At5g19220, At1g27680, At4g39210, and At2g21590, respectively).…”

Isolation and characterization of cDNAs and genomic DNAs encoding ADP-glucose pyrophosphorylase large and small subunits from sweet potato

“…On the contrary, the expressions of LS genes are usually tissue-and development-specific. The expression patterns and regulatory properties of different LS isoforms have been comprehensively studied in tomato (Park and Chung 1998), Arabidopsis (Crevillén et al 2003(Crevillén et al , 2005, and rice , and the results of those studies strongly indicate that AGPase heterotetramers formed in different tissues or organs display distinct kinetic and regulatory properties to control starch biosynthesis. It is suggested that the LSs of agriculturally important crops such as potato and tomato, which have undergone significant selection under both domestication and natural selection, may have evolved novel modulatory characteristics (Petreikov et al 2010).…”

Ostreococcus tauri ADP-glucose Pyrophosphorylase Reveals Alternative Paths for the Evolution of Subunit Roles

“…In plants and green algae, the presence of two types of subunits expanded the sequence space to explore new roles. Recently, it was shown that L subunit isoforms from Arabidopsis had different properties based on the tissue expression (2,10). On the other hand, the presence of two types of subunits may have constrained each subunit to adopt complementary roles.…”