Engineering plants for reduced lignin amount or altered structure is often associated with a yield penalty. Several hypotheses have been put forward to explain the molecular basis of the yield penalty. It has been shown that lignin modification often results in a collapse of vessels, which negatively affects water and nutrient transport in the plant.

When improving plant cell walls, it all comes down to identifying the genes that are involved in the biosynthesis of the major cell wall polymers, and altering their expression levels in target crops such as poplar and maize. Through co-expression analyses in Arabidopsis and maize, we have identified a set of candidate genes that likely play an important role in phenolic biosynthesis.