Cloning of fiber-specific cDNAs and their structural variations in 4 fibermutants

A mRNA preferentially expressed in cotton fiber was cloned from fiber total RNA of normal upland cotton TM-1 (wild-type) by using RT-PCR and correspon ding cDNA (signed as TM-E6) was sequenced, TM-E6 gene had no intron and con tained an open reading frame of 771 bp long, and might encode a peptide of 246 amino acids, Other 4 genes, Fl-E6, Li-E6, N-E6 and Bl-E6, which were ho mologous to TM-E6 gene, were also isolated from 4 fiber mutants of Fiberles s Xu-zhou 142, Ligon lintless, Naked seed and Brown lint, respectively. Seq uence analysis of each of these mutant genes revealed many variations in st ructure and nucleotide composition of gene when compared with the sequence of TM-E6 gene. (i) There was a changeable repetitive segment in which GGCTC A (Gly-Ser) was repeated 3-5 times between the 82nd and the 93rd codons in different mutant genes. Since the change of Gly-Ser repetitive segment occu rred not only in the mutants but also in the wild-type cotton, the repeat f requency might not be associated with the mutation of fiber characteristics . (ii) Among the 4 mutant genes, the percentage of changed codons was 7.05% in Fl-E6, 4.98% in Li-E6, and 4.15% in N-E6 and Bl-E6. It seems that the p ercentage of changed codons in E6 sequence was positively correlated to the degree of fiber morphological variation. (iii) E6 polypeptides of two long -fiberless mutants (Fiberless Xuzhou 142 and Ligon lintless) contained high similar (99.4%) variation in the region of 1-174 amino acids from N-termin us, and those of short-fiberless mutants (Fiberless Xuzhou and naked seed) revealed identical variation in the region of 116th-220th amino acids. It a lso seems that there was a parallel relation between E6 protein variation a nd fiber phenotype mutation, (iv) Li-E6 and Bl-E6 genes also expressed at l ow level in seed coat besides at high level in fiber.