Abstract:

Plant MYB transcription factors are characterized by containing a structurally conserved MYB domain, they play important roles in the regulation of plant development and metabolism. Of them, the R2R3 MYB proteins with two MYB domains are involved in regulating secondary metabolism and cellular morphogenesis. Cotton fibers are single-celled seed trichomes. So far, the molecular process of fiber initiation is poorly understood. However, some transcriptional factors such as MYB genes are responsible to fiber cell initiation. Just like in Arabidopsis, leaf trichome formation is mediated through positive and negative regulators such as GL1 and GL2 encoding MYB transcription factors.
In cotton, several MYB transcription factors have been cloned. Expression of type I genes (GhMYB1, 2, and 3) was detected in all tissues tested, while type II genes (GhMYB4, 5, and 6) process involving many other pathways such as signal transduction and transcriptional regulation. Moreover, GhMYB109, a gene encoding a R2R3 MYB transcription factor, was expressed specifically in fiber initials and elongating fibers. And over-expression of GaMYB2 complemented gl1 phenotype as well as induced seed trichome development in Arabidopsis, suggesting a role of MYB-like transcription factors in cotton fiber cell differentiation. The objective of the study was to clone new MYB genes, further put a foundation to illustrate these genes function in cotton fiber developmental stages. In this paper, a MYB transcription factor gene, GhTF1 was isolated from developmentally different cotton fiber pools of elite material 7235 library. GhTF1 (GenBank No.: EF651783) is a 1 115 bp cDNA, its open reading frame is 771 bp, and encodes a polypeptide containing 256 amino acids. GhTF1 was expressed constitutively in every tissue with different expression levels, e.g. with higher levels in fiber cells at initiation and elongations stages. GhTF1 had conserved coding region in A and D diploid cotton species, G. herbaceum and G. raimondii, however, there existed a large DNA fragment insertion/deletion and base substitutions in their corresponding intron region. Southern blotting analysis showed that there were two copies of GhTF1 in the genome of upland cotton, deducing that the sub-genome A and sub-genome D contain each of them. Using the BC₁ mapping population derived from the hybridization between the upland cotton standard line TM-1 and G. barbadense cultivar Hai7124, and TM-1 as recurrent parent, GhTF1 was located on the chromosome 10.

Key words:

Gossypium, MYB gene, cloning, expression, gene tagging