Can genetic engineering of lignin deposition be accomplished without an unacceptable yield penalty?

The secondary cell wall polymer lignin impedes the extraction of fermentable sugars from biomass, and has been one of the major impediments in the development of cost-effective biofuel technologies. Unfortunately, attempts to genetically engineer lignin biosynthesis frequently result in dwarfing or developmental abnormalities of unknown cause, thus limiting the benefits of increased fermentable sugar yield. In this brief review, we explore some of the possible mechanisms that could underlie this poorly understood phenomenon, with the expectation that an understanding of the cause of dwarfing in lignin biosynthetic mutants and transgenic plants could lead to new strategies for the development of improved bioenergy feedstocks.

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► Manipulation of the phenylpropanoid polymer lignin can improve bioenergy crops but often leads to dwarfing.
► Decreasing lignin leads to vascular collapse, but it is unclear that this is the cause of dwarfing.
► Non-lignin phenylpropanoids may be essential for normal plant growth and development.
► Accumulation of lignin biosynthetic intermediates or byproducts may have toxic effects.
► Dwarfism may be mediated by an active cell wall integrity monitoring pathway.