Characterisation of a cotton gene expressed late in fibre cell elongation

Full-length transcripts corresponding to a cotton fibre-specific cDNA, pFS18, were isolated by cDNA library screening and SI-RACE. The cDNA sequences contained a short open reading frame of only 71 amino acids which showed a limited amount of similarity to lipid transfer proteins. Southern analysis revealed the presence of 4-6 related genes in the tetraploid (AD) G. hirsutum genome, one of which, FS18A, was isolated and shown to contain a short open reading frame which originated from the ancestral A diploid genome. Sequence differences between the gene and the full-length pFS18 cDNA, together with the finding that pFS18 is transcribed from the D diploid genome, demonstrated that FS18A does not encode the abundant fibre-specific transcripts represented by pFS18. However, RT-PCR experiments showed that both pFS18 and FS18A-derived transcripts are present in fibre cells at elevated levels compared with other cotton tissues, with the accumulation of transcripts from both genes being greatest during and after the onset of secondary wall synthesis.