Download Blueprints for Building Plant Cell Walls

Editorial
Blueprints for Building Plant Cell Walls
Elucidating the structure and functional properties
of plant cell walls remains a daunting scientific
challenge. While some experimental hurdles are
common to many areas of plant biology (e.g. the
design of novel assays for gene products of unannotated function), others are compounded in cell
wall research because it involves the study of highly
complex architectures built from secondary gene
products and assembled at the cell’s frontier. Full
genome sequences are providing inventories of an
estimated 10% of genes devoted to the synthesis,
secretion, targeting, assembly, and remodeling of
diverse wall structures made in different cell types
and deposited in distinct regions even around a single
cell. However, we still lack fundamental and complete
knowledge of sequences of wall polysaccharides
beyond their unit structures of 10 sugars or so, as
well as the nature, number, and spacing of cross-links
that connect them. Similarly, many aspects of the
composition and organization of the constituents of
cuticularized and lignified walls remain mysterious.
For example, the targeted deposition of monolignols,
sites of polymerization, and assembly into a crosslinked macromolecule are not at all understood, and
most of our knowledge is inferred from examining
products once the macromolecular structure is dissolved. Furthermore, we know little about the pathways by which polysaccharides and other wall
components transit from their sites of synthesis to
the cell surface. The availability of loss-of-function and
gain-of-function genetic variants provides useful tools
to address function, but our ability to perturb structures and understand the consequences are severely
limited by our knowledge of functional molecular
architectures.
The diversity of wall composition and architecture
found in distinct regions or domains around a cell, in
different tissues, and across taxonomic groups underscores the heterogeneous and dynamic nature of
this cellular compartment and its key importance in
cell growth and differentiation. Not surprisingly, then,
in addition to the structural components of the wall,
the apoplastic environment as a whole and the wallplasma membrane interface are host to large numbers
of proteins with a multitude of functions. These
include many families of receptors, whose responses
may be conditioned by an environment with numerous complex elements, and new components of signal
transduction pathways related to sensing the presence
of pathogens, abiotic conditions, metabolic status, and
structural integrity of the wall are just beginning to
emerge.
Plant cell walls, the source of lignocellulosic biomass, are currently in the spotlight for their value as
feedstocks in the production of ethanol, butanol, and
other advanced biofuels. As global challenges of
energy and food security emerge, use-inspired research into deconstructing cell wall polysaccharides
for fermentation by microbes, digestibility of animal
feed, and nutritional content and quality of grains for
human consumption is a critical component of the
response. We wear cell wall products as natural
fibers, use them as wood and paper products, and
value the textural properties of fruits and vegetables
that they impart. However, this Focus Issue touches
only peripherally on the “four F’s” of food, feed,
fiber, and fuel and rather aims to provide an update
on our fundamental understanding of aspects of cell
wall biology from polymer biosynthesis to their
evolutionary history. In the Update articles presented
in this Focus Issue, the contributors have synthesized
current knowledge of cell wall biogenesis; the
secretion and targeting mechanisms of individual
components such as cellulose synthase; the catalytic
mechanisms of some of the myriad enzyme activities
involved in wall remodeling; the intersection between cell wall molecules, receptors, and signaling
pathways; and the inference of structure-function
relationships from an evolutionary-developmental
perspective. These overviews are complemented by
several highlighted research articles that showcase
new tools to probe the complexity of cell wall
architecture as well as bioinformatic, genetic, and
biochemical analyses of members of large cell wallrelated gene families.
The response to the call for this Focus Issue was
tremendous and will spill over into the next few
volumes of Plant Physiology. These other Updates and
Research Articles will be associated electronically
with this Focus Issue. We believe that this response is
symptomatic of a reenergized research community for
cell wall biology, stimulated but not displaced by useinspired research. Thanks to all of the contributors for
their insights and for showcasing the progress and
challenges of this area. These are exciting times!
Maureen McCann and Jocelyn Rose
Guest Editors
Plant Physiology
www.plantphysiol.org/cgi/doi/10.1104/pp.110.900324
Plant PhysiologyÒ, June 2010, Vol. 153, p. 365, www.plantphysiol.org Ó 2010 American Society of Plant Biologists
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