Characterization of Transcription Factors Regulating Cotton Fiber Elongation

Cottons fibers are derived from extensively elongated seed-born trichomes. In Arabidopsis the trichome regulation pathway includes the GL1-GL3/EGL3-TTG1 core complex and the downstream homeodomain-leucine zipper (HD-ZIP) factor GL2. Interestingly, although accumulating genetic and genomic evidence supports that the MIXTA-type MYB transcription factors play a key role in cotton fiber initiation, a number of cotton GL1-type R2R3 MYBs are highly expressed in cotton fiber cells and they could complement the Arabidopsis gl1 mutants. In addition, GhDEL65, a GL3-type bHLH protein of Upland cotton (Gossypium hirsutum), is also functional in regulating trichome development when expressed in Arabidopsis. Thus the MYB-bHLH-WD40 protein complex exists in cotton fiber, but its function awaits further investigation.

In allotetraploid cotton genomes, there are more than 20 genes encoding the GL2-type HD-ZIP IV factors, among which HOX3 is a key regulator of fiber cell elongation. Down-regulation of GhHOX3 expression in G. hirsutumby RNA interference impaired cotton fiber elongation. GhHOX3 binds to GhHD1, another HD-ZIP protein, resulting in enhanced transcriptional activity, and the gibberellin (GA) repressor DELLA interferes with this interaction by competitive binding to GhHOX3. As DELLA protein is degraded in the presence of increased concentrations of GA, our data provide a mechanical explanation to the role of GA in promoting cotton fiber elongation.

To further dissect the regulatory mechanism of cotton fiber elongation, we surveyed the genes down-regulated in the GhHOX3-silenced cotton, among which one encodes a member the Paclobutrazol Resistance (PRE) family, which are known to promote cell growth. By analyzing cotton genomes, we identified 13 PRE genes in G. raimondii and 26 orthologues in allotetraploid cottons, compared to 5 in cacao. The PRE family expansion and diversification in Gossypiummay have played a role in cotton fiber evolution.

Keywords: Gossypium, cotton fiber, transcription factor complex

Xiao-Ya Chen, Jun-Feng Cao, Bo Zhao, Jin-Quan Huang, Xiao-Xia Shangguan, Ling-Jian Wang

National Key Laboratory of Plant Molecular Genetics, Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200032, China.

Email: xychen@sibs.ac.cn