GbEXPATR, a species-specific expansin, enhances cotton fibre elongation through cell wall restructuring

Summary

Cotton provides us the most important natural fibre. High fibre quality is the major goal of cotton breeding, and introducing  genes  conferring  longer, finer and stronger fibre from Gossypium barbadense to Gossypium hirsutum is an important breeding strategy. We  previously  analysed  the  G. barbadense fibre development mechanism by gene expression  profiling  and  found  two  homoeologous fibre-specific  α-expansins  from  G. barbadense,  GbEXPA2 and GbEXPATR.  GbEXPA2 (from the DT genome)  is  a  classical α-expansin, while its homoeolog, GbEXPATR (AT genome), encodes a truncated protein lacking the normal C-terminal polysaccharide-binding domain of other α-expansins and is specifically expressed in G. barbadense.  Silencing  EXPA  in  G. hirsutum induced shorter fibres with thicker cell walls. GbEXPA2 overexpression  in  G. hirsutum  had  no effect  on  mature  fibre length, but produced fibres with a slightly thicker wall and increased crystalline  cellulose content.  Interestingly,  GbEXPATR overexpression resulted in longer, finer and stronger fibres coupled with significantly thinner cell walls. The longer and thinner fibre was associated with lower  expression  of  a  number of  secondary  wall-associated  genes,  especially  chitinase-like  genes, and walls with lower  cellulose  levels  but higher  noncellulosic  polysaccharides   which  advocated  that  a  delay in the transition to secondary  wall  synthesis  might  be  responsible  for  better  fibre. In  conclusion, we propose that α-expansins play a critical role in  fibre development  by  loosening the cell wall;  furthermore,  a  truncated form, GbEXPATR, has a more dramatic effect  through  reorganizing  secondary  wall synthesis and metabolism and should be a candidate gene for developing G. hirsutum cultivars with superior fibre quality.

http://onlinelibrary.wiley.com/doi/10.1111/pbi.12450/abstract?campaign=wolearlyview