Cotton is one of the major cash crops widely planted in over 80 countries mainly for fiber. Cotton fibers, the most important natural material for textile industry, are extremely long, single-celled seed-born trichomes.

Research group led by Professor CHEN Xiaoya at the Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences of the Chinese Academy of Sciences isolated a cotton fiber elongation gene, GhHOX3. 

Scientists, in particular the Ph.D. candidate SHAN Chun-Min, found that the gene, localized to the 12th homoeologous chromosome set and associated with quantitative trait loci (QTLs) for fiber length, encodes a homeodomain-leucine zipper (HD-ZIP) transcription factor. Silencing of GhHOX3 dramatically reduces fiber length, whereas its overexpression leads to longer fiber.  

GhHOX3 regulates target genes, including the cell wall loosening protein genes GhRDL1 and GhEXPA1, by binding to the L1-box in the promoter. GhHOX3 interacts with GhHD1, another homeodomain protein and with cotton DELLA protein GhSLR1, a major repressor of the growth hormone gibberellin (GA). GA enhances GhHOX3 activity and fiber cell growth through degrading GhSLR1. 

The key regulator of cotton fiber elongation was identified for the first time. The direct interaction between DELLA and a specific homeodomain protein sheds new light on the biochemical mechanism of GA, a widely acknowledged green evolution hormone, in controlling plant cell elongation. 

This study entitled “Control of cotton fiber elongation by a homeodomain transcription factor GhHOX3” was published in Nature Communications. 

The project was supported by grants from the State Key Basic Research Program of China, Chinese Academy of Sciences and the National Major Project. 

A model for the regulation of cotton fiber elongation by GhHOX3 and the phytohormone GA. (Image by SHAN et al.)