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Title: Characterization of an ADP-glucose Pyrophosphorylase Small Subunit Gene Expressed in Developing Cotton (Gossypium hirsutum) Fibers

item Taliercio, Earl

Submitted to: Molecular Biology Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/15/2010
Publication Date: 1/29/2010
Citation: Taliercio, E.W. 2010. Characterization of an ADP-glucose Pyrophosphorylase Small Subunit Gene Expressed in Developing Cotton (Gossypium hirsutum) Fibers. Mol Biol Rep. DOI:10.1007/s11033-010-9961-0.

Interpretive Summary: Cotton stores starch in its stems and roots that is redistributed to developing bolls to support seed and fiber development. Accumulation of starch in cotton vegetative tissues and fibers is likely to play a role in cotton development. Starch accumulation also plays a role in cell expansion. A gene encoding a cotton ADP-glucose pyrophosphorylase (ADPGp) gene was isolated, sequenced and characterized. ADPGp is an important enzyme controlling starch biosynthesis. The gene had a structure consisting of 8 introns and 9 exons, similar to other plant AGPGp genes. The protein that the gene encoded also had many features similar to other plant ADPGp including a variable amino end, conserved catalytic sites and conserved amino acid sequences that control enzyme activity. This gene differs from a previously characterized cotton ADPGp gene because it was not abundantly expressed in starch storing roots but was expressed in developing fiber. Starch was also found and measured in elongating fibers. Analysis of the promoter region failed to identify a complete basal promoter but did identify sequences indicating that expression of this gene may respond to various phytohomones and light regimes.

Technical Abstract: ADP-glucose pyrophosphorylase (ADPGp) plays a rate limiting role in the biosynthesis of starch and has been shown to be involved in cell expansion of tobacco sepals. A cotton gene encoding ADPGp small subunit was isolated and sequenced. The gene contains 8 introns similar to other ADPGp genes. The open reading frame (ORF) was very similar to other plant ADPGp small subunits including conserved sites associated enzyme activity, with allosteric regulation by phosphoglyceraldehyde and phosphate and with redox regulation and substrate binding. In silico sequence analysis of the promoter region of the gene identified motifs associated with light regulation, circadian response, endosperm expression, ethylene response and gibberellic acid response. Quantitative rt-PCR (QPCR) analyses indicated this gene increased in expression in leaves and young fiber but not in starch-storing roots. Levels of mRNA encoding the ADPGp large subunit and levels of starch were also higher in young fibers relative to older fibers.