Biology Reference
In-Depth Information
VII. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
ABSTRACT
As we transition into the twenty-first century, the need for renewable resources to
address global energy and food demands has become a major concern. Around the
world, scientists are interested in engineering dedicated biomass feedstocks particu-
larly for improved cell wall composition by modifying the major wall components,
cellulose and lignin. In this chapter, we review the current knowledge of plant
engineering specifically in the area of lignin biosynthesis and composition towards
the goal of generating plants optimized for bioethanol production and animal feed.
Crops dedicated as biomass feedstocks, i.e., miscanthus, switchgrass, triticals, sor-
ghum and maize, are grasses, which have unique characteristics of making their cell
walls ideal sources for bioethanol production. Our understanding of the grass cell wall
has significantly improved in the past two decades through studies carried out
primarily in maize (Zea mays). Here, we discuss several aspects of lignin deposition
into the cell wall including the cellular and molecular aspects of lignin biosynthesis.
Significant effort was dedicated to identifying the molecular regulators of these
processes and the developmental defects resulting from gene modifications. In addi-
tion, we demonstrate genetic correlations between genes of the lignin biosynthesis
pathway to those involved in cell wall deposition using a gene expression network
program. Together this work lays the foundation for future studies addressing the
molecular regulation of lignification in the grasses in hopes to develop, through
genetic engineering, ideal biomass feedstocks for biofuel production.
I. INTRODUCTION
Throughout history, grass has played an important role in agriculture serving
as plant-derived food and fuel resources. Today, cereal grasses, that is, wheat
and maize, are arguably the world's most important commodities, particularly
due to the rise in human population which directly translates into increased
food consumption. In addition, an elevation in energy usage has resulted,
particularly in developing countries, igniting the shift from the limited and
rapidly depleting petroleum-based energy sources in use today to those gener-
ated from renewable sources, that is, wind, solar and lignocellulosic plants.
Therefore, alternative energy sources, separate from those obtained from non-
renewable carbon-based resources, are needed for the twenty-first century.
Energy derived from plants is not a novel concept however, this technique
has been revisited on a larger scale particularly over the past 20 years. One
example is found in Brazil where ethanol produced from sugarcane has replaced
petroleum-derived oil for their transportation needs. In 2008, bioethanol con-
sumption as a fuel surpassed gasoline (
Chaddad, 2010
). Indeed, sugarcane is
