Biology Reference
In-Depth Information
VI. The Specific Regulation of the Syringyl Pathway. . . . . . . . . . . . . . . . . . . . . . . . . 193
VII. Combinatorial Transcriptional Complexes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194
VIII. Environmental Regulation of the Lignin Biosynthetic Pathway. . . . . . . . . . 196
IX. Hormonal Control and Regulation of Lignin Biosynthesis. . . . . . . . . . . . . . . 198
X. Concluding Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210
ABSTRACT
The discovery that AC elements coordinated the regulation of genes belonging to the
entire lignin biosynthetic pathway was the first breakthrough in understanding how
lignin biosynthesis is regulated. Since then, tremendous progress has been made
in the identification and characterization of many transcription factors (TFs) that
regulate the genes of the phenylpropanoid branch pathway leading to lignin. A major
breakthrough consisted in the discovery of a hierarchical transcriptional network
regulating the biosynthesis of lignified secondary walls (SWs) in Arabidopsis.The
NAC TFs (VND/NST/SND) work as the first layer of master switches activating the
whole SW biosynthetic network through the regulation of a cascade of downstream
TFs. Among these, MYB46/83 act as a second layer of master switches. Recent
findings, however, reveal that the regulation of SW formation is far more complex
than initially thought, involving both positive and negative regulators, dual function
regulators, feedback loops, combinatorial complexes and cross talk between pathways.
Finally, because of the great potential that lignocellulosic biomass represents for the
production of bioenergy, there is a great interest in further elucidating the molecular
mechanisms underlying the regulation of lignified SW and subsequently applying this
knowledge to improve their saccharification potential for the generation of biofuels.
I. INTRODUCTION
Of the numerous adaptations that land plants have developed for their
successful existence on earth, the appearance of the phenylpropanoid path-
way has been a crucial event allowing them to successfully face important
challenges including desiccation stress, temperature stress, UV radiation as
well as herbivore and pathogen attacks. The ability to deposit phenylpropa-
noid lignins in secondary cell walls (SWs) allowed the further development of
large upright plants adapted to a terrestrial habitat ( Weng and Chapple, 2010
and references therein). Lignin provided mechanical support for tracheo-
phytes allowing them to stand upright and strengthened and waterproofed
the water-conducting tracheary elements allowing them to withstand the
negative pressure generated during transpiration. Lignification transformed
the phenylpropanoid metabolism into a major sink for carbon in plants,
eclipsed only by cellulose, and it has now estimated that lignin represents as
much as 30% of the total biomass produced in the biosphere ( Boerjan et al.,
2003 ). Lignin is an aromatic polymer derived from the oxidative polymeriza-
tion of three monomers; p-coumaryl, coniferyl and sinapyl alcohols giving raise
Search WWH ::




Custom Search