Gene Expression of ADP-glucose Pyrophosphorylase and Starch Contents in Rice Cultured Cells are Cooperatively Regulated by Sucrose and ABA

Abstract

Six cDNA clones encoding two small subunits and four large subunits of ADP-glucose pyrophosphorylase (AGPase) were mined from the database of rice full-length cDNAs, cloned and subsequently named: OsAPS1, OsAPS2, OsAPL1, OsAPL2, OsAPL3 and OsAPL4. Expression patterns of the six genes were examined by Northern blot analysis with gene-specific probes. OsAPL3 was predominantly expressed in the middle phases of seed development, and OsAPS1, OsAPL1 and OsAPL2 were expressed later in seed development. OsAPS2 and OsAPL4 were constitutively expressed and these isoforms were coordinated with starch accumulation in the developing rice seed. In order to clarify the effect of sugars and plant hormones on AGPase gene expression more precisely, a rice cell culture system was used. OsAPL3 transcript significantly accumulated in response to increased levels of sucrose and abscisic acid (ABA) concentration in the medium; however, the transcripts of other AGPase genes did not show significant accumulation. Under identical conditions, starch contents in the cultured cells also increased. Interestingly, ABA alone did not affect the gene expression of OsAPL3 and starch content. Collectively, these results indicated that the expression level of OsAPL3 and starch content in the cultured cells were cooperatively controlled by alterations in the concentration of both sucrose and ABA.

The Two AGPase Subunits Evolve at Different Rates in Angiosperms, yet They Are Equally Sensitive to Activity-Altering Amino Acid Changes When Expressed in Bacteria

“…The major small subunits in barley (Hordeum vulgare) endosperm and leaves (Thorbjørnsen et al, 1996;Johnson et al, 2003;Rosti et al, 2006) are encoded by a single gene that is alternatively spliced, while the interacting large subunits are encoded by different genes. Expression patterns and functional characterization of large and small subunits from tomato, potato, barley, rice, and Arabidopsis indicate that large subunits are more tissue specific than are small subunits (La Cognata et al, 1995;Park and Chung, 1998;Akihiro et al, 2005;Crevillen et al, 2005;Ohdan et al, 2005;Rosti et al, 2006). Taken as a whole, these results strongly suggest that the large subunit genes, in comparison to small subunit genes, underwent more successful duplications that were then followed in some cases by subfunctionalization in their expression pattern.…”

“…Perusal of the rice (Oryza sativa), Populus (Populus trichocarpa), and Arabidopsis thaliana completed genomes suggests that the large subunit genes underwent more successful duplications than did the small subunit genes. The Arabidopsis genome contains a single functional gene for the AGPase small subunit but four genes for the large subunit (Crevillen et al, 2003(Crevillen et al, , 2005, rice contains two small subunit genes and four large subunit genes (Akihiro et al, 2005;Ohdan et al, 2005), and Populus apparently has one small and six large subunit genes (Tuskan et al, 2006). Three large subunit genes and one small subunit gene have been isolated from tomato (Solanum lycopersicum) and potato (La Cognata et al, 1995;Park and Chung, 1998).…”

Causal Relations Among Starch Biosynthesis, Structure, and Properties

“…AGPase subunits are encoded by multiple genes. For example, in rice AGP-L is encoded by four genes: OsAGPL1, OsAGPL2, OsAGPL2, and OsAGPL4, while AGP-S is encoded by two genes: OsAGPS1 and OsAGPS2 [1]. These genes express differently in different botanical organs, which means that the composition of AGPase subunits may vary in different parts of the same plant [129,187].…”

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

“…Nakatani and Komeichi (1992) reported a positive correlation between AGPase activity and the starch content in the tuberous roots of sweet potato. Three mechanisms are known to regulate AGPase activity: (i) transcriptional regulation (Müller-Röber et al, 1990;Sokolov et al, 1998;Akihiro et al, 2005;Nagata and Saitou, 2009); (ii) allosteric regulation, via glycerate-3-phosphate and inorganic phosphate (Sowokinos and Preiss, 1982); and (iii) post-translational redox modifi cation in response to sugars (Tiessen et al, 2002;Hendriks et al, 2003;Michalska et al, 2009). AGPase is a heterotetramer in higher plants and is composed of two large and two small subunits (Morell et al, 1987).…”