Submitted to: Planta
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/22/2003
Publication Date: 11/25/2003
Citation: Kim, H.J., Triplett, B.A. 2004. Cotton-fiber germin-like protein I. Molecular cloning and expression. Planta. 218:516-524. Interpretive Summary: For most of the commercially important types of cotton there are two types of fibers: lint fibers that are used in yarn and fabric construction and the shorter fuzz fibers that are used in non-woven textiles and as substrates for manufacturing plastics and rayon. Our goal is to reduce the number of fuzz fibers and increase the number of lint fibers per seed. Both of these approaches will impact fiber quality and yield. The work presented in this paper characterizes one gene that is actively synthesized in normal cotton seeds and is not synthesized in a mutant line where the production of fuzz fiber is blocked and development of lint fiber is restricted to one area of the seed. This newly identified cotton fiber gene is similar to several other genes previously characterized from other plants, however, the function of this gene product in plant development is unknown at present. From our study, the abundance of this gene's messenger ribonucleic acid is correlated with the most active periods of fiber cell expansion suggesting that this gene is likely to be important for initiation of fiber development and determination of fiber length. Other factors that influence when the gene is "read" have also been identified by this work. This information will be used by researchers to design specific probes for determining when the protein is produced and where the protein is localized in the cell.
Technical Abstract: A cotton (Gossypium hirsutum, L.) homologue of germin-like proteins was isolated by differential display analysis comparing early stages of cotton fiber development between a wild type line, Texas Marker-1 (TM1) and a near isogenic mutant, Naked Seed (N1). Transcripts of the cotton germin-like protein (GhGLP1) were expressed specifically in the immature seeds of TM1, but were not expressed in the mutant although the GhGLP1 gene was present in both lines. The deduced protein sequence of GhGLP1 is most homologous to an Arabidopsis GLP in subfamily 3 (AtGLP3a), Prunus persica auxin-binding proteins (ABPs), and two different classes of hydrogen peroxide-producing enzymes: wheat germin oxalate oxidase and moss extracellular Mn-SOD. Cotton GLPs constitute a multigene family like those of Arabidopsis and rice. Contrary to the expression pattern of germins and GLPs involved in defense mechanisms, biotic and abiotic stresses down-regulated expression of the GhGLP1 transcript. Despite the considerable sequence homology with germin oxalate oxidase, GhGLP1 does not have oxalate oxidase activity. Expression of GhGLP1 was fiber-specific and developmentally regulated. Transcripts of GhGLP1 accumulated to their highest levels during the period of fiber expansion, followed by a sharp decline when the rate of cell expansion decreases. Numerous functions have been proposed for dicot GLPs, however, to date, there is no direct evidence for how these proteins function in vivo. The association of maximal GhGLP1 expression with stages of maximal cotton fiber elongation suggests that some GLPs are important for cell wall expansion.