GhTUB17 play an important role in fiber growth and might involve in fiber elongation induced by brassinosteroids

Functional Genomics

poster

zhai, yunlan; li, fang; wei, ting; ye, shu-e; zou, chuang; tang, ying-cai; zeng, zhi-feng; luo, ming

zhai, yunlan; li, fang; wei, ting; ye, shu-e; zou, chuang; tang, ying-cai; zeng, zhi-feng

luo, ming

Plant microtubule cytoskeleton plays an important role in cell elongation and cell wall formation. The orientation of cortical microtubule array was consistent well with cellulose microfibril. At cell elongation period, transverse microtubule array is observed while longitudinal and oblique array present in cell stopped elongation. In cotton fiber cell, one of the longest cells ever characterized in plant kingdom, it is closely related between the arrangement of cortical microtubules and fiber cell elongation. The major component of microtubules is heterodimer of highly conserved α- and β-tubulin. There were 12 α-tubulin genes and 19 β-tubulin genes in cotton genome and some genes expressed preferentially in fiber cell or a certain developmental stage of cotton fiber. These indicated that tubulin gene had an important role in the growth and development of fibers. However, the function and mechanism of each tubulin gene in fiber development is largely unknown to date. To illuminate their function in fiber cell elongation, we have examined the expression difference of 31 microtubule genes between ligon lintless-1 (li-1) mutant and it’s isogenic wild-type TM-1 by quantitative real-time RT-PCR. The li-1 has extremely short fibers and was employed as an ideal material to study fiber elongation. The expression of GhTUB17, one of the β-tubulin genes, was drastically suppressed in 10 DPA fibers of li-1 mutant. The gene specifically expressed in fiber cell and the expression peak present in 6 and 8 DPA fibers. Moderate expression level was in 10 and 12 DPA fibers while the transcript was hardly detected in the fiber after 14 DPA. These results revealed that the GhTUB17 primarily related to fiber elongation. The length of cDNA of GhTUB17 was 1475bp in upland cotton (Gossypium hirsutum). It contains a 1335bp ORF encoding 444 amino acid residues with a molecular weight of 50kD. isoelectric point was 4.65. The amino acid sequence was high homology with the β-tubulin from Arabidopsis thaliana, tobacco, and cocoa. However, GhTUB17 was in a specific branch in phylogenetic tree. It was suggested that the gene might play a special role in fiber cell development. To further elucidate the mechanism of expression decrease in 1i-1 fiber, the cDNAs, genomic DNAs, and about 2.5 kb promoter sequences of GhTUB17 gene were cloned both from li-1 and TM-1. There was little diversity in the cDNA and genomic sequence while an 180bp deletion was in the promoter from li-1 mutant. Five brassinosteroid response elements were in the fragment. Correspondently, the expression of GhTUB17 was significantly induced by Brassinolide (BL) treatment in wild type fibers while less response for BL treatment in li-1 fibers. These results indicate that GhTUB17 play an important role in fiber growth and might involve in fiber elongation induced by brassinosteroids. Keywords: cytoskeleton; GhTUB17 gene; cotton fiber; li-1 mutant; brassinosteroid