A cotton gene encoding novel MADS-box protein is preferentially expressed in fibers and functions in cell elongation

Cotton fibers, as natural fibers, are widely used in the textile industry in the world. In order to find genes involved in fiber development, a cDNA （designated as GhMADSll） encoding a novel MADS protein with 151 amino acid residues was isolated from cotton fiber cDNA library. The deduced protein shares high similarity with Arabidopsis AP1 and AGL8 in MADS domain. However, the GhMADSll protein （being absent of the partial K-domain and normal C-terminus） is shorter than AP1 and AGL8 by the reason of gene frameshift mutation during evolution. The experimental results revealed that GhMADSll was not a transcriptional activator, and it did not form homodimer. GhMADSll transcripts were specifically accumulated in elongating fibers, but no or very low signals of its expression were detected in other tissues of cotton. Overexpression of GhMADSll in fission yeast promotes atypical cell elongation by 1.4-2.0-fold. Furthermore, morphological analysis indicated that the transformed cells expressing GhMADSllm, a MIKC-type derivative of GhMADSll by the site-directed mutation, displayed the same phenotype as that of the transformed cells with GhMADSll. The concurrence of these data sets suggested that GhMADSll protein may function in fiber cell elongation, and its MADS domain and partial K- domain are sufficient for this function.