Cotton fiber germin-like protein. I. Molecular cloning and gene expression

The presence of cotton (Gossypium hirsutum L.) fiber transcripts coding for a germin-like protein (GLP) was revealed by differential display analysis in which early stages of cotton fiber development between a wild type line, Texas Marker-1 (TM1) and a near isogenic mutant, Naked Seed (N1) were compared. Transcripts of the cotton GLP (GhGLP1) accumulated specifically in TM1, but did not accumulate in the mutant although the GhGLP1 gene was present in both lines. The deduced protein sequence of GhGLP1 is similar to Prunus persica auxin-binding proteins, a barley ADP-glucose pyrophosphatase/phosphodiesterase and two different classes of hydrogen peroxide-producing enzymes: wheat germin oxalate oxidase and moss extracellular Mn-superoxide dismutase. Cotton GLPs constitute a multigene family like those of Arabidopsis, rice, soybean, and barley. GhGLP1 transcripts accumulated to their highest levels during the period of fiber expansion, followed by a sharp decline when the rate of cell expansion decreased. While germins and GLPs appear to be involved in defense mechanisms in some plants, both biotic and abiotic stress down-regulated the expression of GhGLP1. Numerous functions have been proposed for dicot GLPs. However, to date, there is little 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 may be important for cell wall expansion.