Biology Reference
In-Depth Information
published studies filled these gaps and included microarray data from tissues
enriched in lignin content (
Guillaumie et al., 2007a,b, 2008
). Microarray data
relative to cell wall components, including lignins, are available for some grass
species, such as maize. Web portals similar to MAIZEWALL (
http://www.
polebio.lrsv.ups-tlse.fr/MAIZEWALL/
)
may help to highlight genework mod-
ifications in plants. Unfortunately, these initiatives are scarce and may become
obsolete if not updated. Therefore, co-expression analysis like PlaNet database
(
Mutwil et al., 2011
) may be used to rapidly identify genes associated with
genes of interest as exemplified above with PAL gene family.
Cross-species co-expression analysis has additional advantages by high-
lighting conserved and, thus, potentially significant participants of biological
processes of interest. Another important feature of cross-species analysis is
the ability to identify functional homologs between species, which is essential
when accumulated knowledge from model organism needs to be transferred
to non-model organisms. The analysis correctly identified major components
of lignin biosynthesis pathway and also suggested several new putative
components, especially whether the lignin pathway is different in grasses as
compared to dicotyledons as suggested by preliminary data.
A potential weakness and the same advantage of the analysis is the
inability to distinguish tightly coupled biological processes. Phenylalanine,
cellulose and lignin biosynthesis seem to be tightly coupled, which is plausi-
ble, since phenylalanine is consumed during lignin formation and needs to be
constantly replenished to preserve metabolic homeostasis. Also, the majority
of lignin is deposited in secondary cell walls that are rich in lignocellulose,
requiring those two processes to be coordinated.
VII. CONCLUSION
Our understanding of lignification of the grass cell wall, including biosynthe-
sis and deposition, has improved significantly over the past two decades.
Although several aspects of these processes are conserved between dicotyle-
dons and grasses, clear differences in composition are observed. As detailed
above, one major example of the differences can be found in the abundance
of FA in grass cell walls. The high amount of FA impacts the initial steps
of lignin polymerization leading to the hypothesis that these molecules are
involved in determining the sites of nucleation for lignification. Interestingly,
FA is found in low quantities in dicotyledons, suggesting that different
biological processes are involved in lignin polymerization in these plants.
Additional questions remain concerning grass cell wall lignification including
whether pCA serves an additional role in grass cell walls; how feruloylation
