Biology Reference
In-Depth Information
C. Stem Laccases: First In Vivo Evidence Implicating Laccases in Lignin
Polymerization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156
D. Flavonoid Polymerization in Seeds: Other Roles for
Arabidopsis Laccases, Namely, TRANSPARENT TESTA 10/
AtLAC15......................................................................... 159
IV. Transcriptional Regulation of Plant Laccases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161
V. Conclusion and Perspectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167
ABSTRACT
Laccases are ubiquitous oxidases present in animals, plants, bacteria, and fungi.
In plant species, they occur as large multigenic families. The involvement of
peroxidases in lignification is supported by a wealth of literature data. In contrast,
the role of laccases in this major plant process is less firmly established. The large
number of plant laccases, which argues for a variety of functions in plant develop-
ment, makes the identification of lignin-specific laccases a challenge. However, in
the past decade, the development of new genetic technologies and tools has played a
central role towards resolving this issue. In addition, the plant model, Arabidopsis
thaliana, has recently provided novel insights about the occurrence of laccases
involved in stem lignification. Information about lignin-related laccases is also
available from other species, such as poplar, or other organs and tissues, such
as seed coats. This review brings a short and cutting edge survey of laccases and
lignification.
I. INTRODUCTION
Lignins are complex cell wall polymers mainly constituted of para-
hydroxyphenyl (H), guaiacyl (G), and syringyl (S) units derived from pre-
cursors known as monolignols. These precursors are synthesized in the
cytoplasm and then transported to the cell wall where polymerization occurs
( Simmons et al., 2010 ). The oxidative polymerization of monolignols in plant
cell walls has been reported to be enzymatically supported by plant oxidases,
peroxidases, and/or laccases ( Mayer and Staples, 2002 ). Over the past two
decades, efforts have been made to more precisely identify the genes involved
in lignin polymerization but until recently the precise role of laccases in
lignification was still ill-defined. This review brings a short and up-to-date
survey about the involvement of plant laccases in this important plant
process.
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