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

Abstract

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 corresponding cDNA (signed asTM-E6) was sequenced.TM-E6 gene had no intron and contained 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 andBl-E6, which were homologous toTM-E6 gene, were also isolated from 4 fiber mutants of Fiberless Xu-zhou 142, Ligon lintless, Naked seed and Brown lint, respectively. Sequence analysis of each of these mutant genes revealed many variations in structure and nucleotide composition of gene when compared with the sequence ofTM-E6 gene. (i) There was a changeable repetitive segment in which GGCTCA (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 occurred not only in the mutants but also in the wild-type cotton, the repeat frequency might not be associated with the mutation of fiber characteristics, (ii) Among the 4 mutant genes, the percentage of changed codons was 7.05% inFl-E6, 4.98% inLi-E6, and 4.15% inN-E6 andBl-E6. It seems that the percentage of changed codons inE6 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-terminus, and those of short-fiberless mutants (Fiberless Xuzhou and naked seed) revealed identical variation in the region of 116th–220th amino acids. It also seems that there was a parallel relation between E6 protein variation and fiber phenotype mutation, (iv)Li-E6 andBl-E6 genes also expressed at low level in seed coat besides at high level in fiber.