Molecular cloning and localization of a novel cotton annexin gene expressed preferentially during fiber development.

Annexins constitute a family of multifunction and structurally related proteins. These proteins are ubiquitous in the plant kingdom, and are important calcium-dependent membrane-binding proteins that participate in the polar development of different plant regions such as rhizoids, root caps, and pollen tube tips. In this study, a novel cotton annexin gene (designated as GhFAnnx) was isolated from a fiber cDNA library of cotton (Gossypium hirsutum). The full-length cDNA of GhFAnnx comprises an open reading frame of 945 bp that encodes a 314-amino acid protein with a calculated molecular mass of 35.7 kDa and an isoelectric point of 6.49. Genomic GhFAnnx sequences from different cotton species, TM-1, Hai7124 and two diploid progenitor cottons, G. herbaceum (A-genome) and G. raimondii (D-genome) showed that at least two copies of the GhFAnnx gene, each with six exons and five introns in the coding region, were identified in the allotetraploid cotton genome. The GhFAnnx gene cloned from the cDNA library in this study was mapped to the chromosome 10 of the A-subgenome of the tetraploid cotton. Sequence alignment revealed that GhFAnnx contained four repeats of 70 amino acids. Semi-quantitative reverse transcriptase-polymerase chain reaction revealed that GhFAnnx is preferentially expressed in different developmental fibers but its expression is low in roots, stems, and leaves. Subcellular localization of GhFAnnx in onion epidermal cells and cotton fibers suggests that this protein is ubiquitous in the epidermal cells of onion, but assembles at the edge and the inner side of the apex of the cotton fiber tips with brilliant spots. In summary, GhFAnnx influences fiber development and is associated with the polar expansion of the cotton fiber during elongation stages.