A silkworm gene for fibroin was introduced into the upland cotton WC line by Agrobacterium-mediated transformation. PCR detection for fibroin, nptII and gus genes, Kanamycin (Km)-resistance analysis and GUS-histochemical assay were conducted on 30 regenerated plants from 9 callus lines, and 17 positive plants were obtained by these 5 screening methods. By Km-resistance analysis and PCR for fibroin, 6 homozygous lines in T3 were obtained. Southern blot and Northern bolt demonstrated that the fibroin gene was inserted into the genome of these 6 lines, stably inherited and expressed. Compared to the control, the surface structure of mature fiber in the 6 lines was significantly distorted and an increased number of convolution was observed by scanning electron microscopy (SEM). Fiber quality traits analysis indicated that fiber elongation of the 6 homozygous lines was all increased and fiber strength of 3 lines was enhanced. These results indicated that fibroin expression influenced cotton fiber structure and quality, suggesting that fibroin has great potential for improving cotton fiber quality by genetic engineering.

Ten genes expressed preferentially in fiber development period reported previously and 14 cotton cultivars (strains) with distinctly different fiber quality were selected in this paper. To test the relative expression values of the genes in six different fiber developmental stages, 0 day post anthesis (DPA), 5DPA, 10DPA, 15DPA, 20DPA, 23DPA, by real-time quantitative RT-PCR (qRT-PCR), and the data of fiber qualities from 14 cotton varieties (strains). The expression profile showed that GhExp1, GhCIPK1, GhSus1, GhSusA1, and GhPL genes were expressed preferentially during fiber elongation; GhACT1, GhRacA, and GhRacB genes all had high expression level in earlier stage of fiber elongation and the thickening period of secondary cell wall. Two cellulose synthase genes (GhCelA1 and GhCelA3) were expressed predominantly during late stage of fiber elongation and the thickening period of secondary cell wall. For most genes, the expression value in low expression level period had significant correlation with fiber quality, while no significant correlation was detected in preferential expression stage of these genes with an exception of GhRacA gene. The expression level of GhExp1 in 20DPA fiber of 14 cotton varieties (strains) had a significant negative correlation with fiber strength and uniformity and a significant positive correlation with fiber elongation percentage; the expression level of GhPL gene in 23DPA had a significant negative correlation with fiber length; the expression level of GhRacA gene in 5DPA and 23DPA both had a high significant positive correlation with fiber elongation percentage; the expression level of GhRacB gene in 10DPA had a significant negative correlation with fiber length and uniformity; the expression level of GhCelA1 gene in 5DPA had a significant positive correlation with fiber length and a significant negative correlation with micronaire value; the expression level of GhCelA1 gene in 10DPA had a significant negative correlation with fiber length, a significant positive cor-relation with micronaire value, and a high significant correlation with fiber elongation percentage; the correlation between the expression levels of GhCIPK1, GhACT1, GhSus1, GhSusA1and GhCelA3 gene and fiber quality indexes had not been detected.