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