Disrupting Flavone Synthase II Alters Lignin and Improves Biomass Digestibility

In previous studies, it was found that cereals use tricin, a flavonoid, as a co-monomer with monolignols for cell wall lignification. Lydia Lam Pui-ying from the University of Hong Kong, and colleagues inhibited the production of tricin in rice through genetic engineering of OsFNSII, a rice flavone synthase gene, in to make it easier to break down cellulose. Studies have previously established that flavone synthase II is vital for the synthesis of tricin metabolites in rice (Oryza sativa L.).

The team developed a tricin-deficient mutant rice plant (fnsII mutant) and analyzed its cell wall structure and properties. The mutant has similar growth habit with the wild types. However, chemical and NMR structural analyses demonstrated that the mutant lignin is completely devoid of tricin, indicating that flavone synthase II activity is essential for deposition of lignin in rice cell walls.

The mutant also showed substantially reduced lignin content. The fnsII mutant was also revealed to have enhanced enzymatic saccharification efficiency, suggesting that cell wall recalcitrance of grass biomass may be reduced through manipulation of flavonoid monomer supply for lignification.