Lignin bioengineering.

Lignin is one of the most abundant aromatic biopolymers and a major component of plant cell walls. It occurs via oxidative coupling of monolignols, which are synthesized from the phenylpropanoid pathway. Lignin is the primary material responsible for biomass recalcitrance, has almost no industrial utility, and cannot be simply removed from growing plants without causing serious developmental defects. Fortunately, recent studies report that lignin composition and distribution can be manipulated to a certain extent by using tissue-specific promoters to reduce its recalcitrance, change its biophysical properties, and increase its commercial value. Moreover, the emergence of novel synthetic biology tools to achieve biological control using genome bioediting technologies and tight regulation of transgene expression opens new doors for engineering. This review focuses on lignin bioengineering strategies and describes emerging technologies that could be used to generate tomorrow's bioenergy and biochemical crops.