Biology Reference
In-Depth Information
gymnosperms lack both F5H and NST1/SND1 orthologs, but they do have
orthologs of AtMYB46 and AtMYB58. The authors proposed that both F5H
and NST1 appeared at a similar time after the divergence of angiosperms and
gymnosperms, with F5H possibly originating as a component of a defence
mechanism that was recruited to cell wall biosynthesis through the evolution of
NST1-binding elements in its promoter (
Zhao et al.,2010b
).
It is worth noting that in contrast to the F5H from Arabidopsis, the
promoter of the maize F5H is recognized and bound in vivo by a MYB factor,
ZmMYB31 as demonstrated by ChIP experiments (
Fornal´ et al., 2010
). This
suggests an evolutionary divergence between the regulation of the maize and
the A. thaliana F5H genes by R2R3-MYB factors. ZmMYB31 is a negative
regulator of lignin biosynthesis and its overexpression in A. thaliana also
induces the expression of several stress-responsive proteins.
Interestingly, independent origins of S lignin in vascular plants have
recently been reported by
Weng et al. (2008)
. F5H has evolved independently
in two major plant lineages, lycophytes and angiosperms, which diverged
from one another more than 400 million years ago. F5H from Selaginella
moellendorffii (SmF5H) is functionally equivalent but phylogenetically inde-
pendent from angiosperm F5H. Both AtF5H and SmF5H can catalyse
5-hydroxylation reactions on G-substituted intermediates equally well but
SmF5H can also efficiently catalyse the 3-hydroxylation of p-coumaraldehyde
and p-coumaryl alcohol (
Weng et al.,2010
). Thus, a unique phenylpropanoid
dual meta-hydroxylase, SmF5H, evolved in the lycophyte Selaginella where
it mediates S lignin biosynthesis via a C3H-independent pathway. The inde-
pendent occurrence of S lignin in distant lineages might correspond to evolu-
tionary advantages such as increased mechanical strength and/or selective
advantage in defence against pathogens. S lignin is indeed an important
component of the resistance response in wheat (
Menden et al.,2007
).
VII. COMBINATORIAL
TRANSCRIPTIONAL COMPLEXES
Understanding protein-protein interactions is crucial to learn more about how
regulatory gene activity is regulated so as to integrate developmental and
environmental signals and to activate or repress target genes in appropriate
cellular types. Only a small number of reports exist regarding protein-protein
interactions and the regulation of the lignified SW. One of the most studied
examples of phenylpropanoid metabolism-related protein-protein interaction
was discovered following work on the colour changes due to alterations in
anthocyanin accumulation in plant seeds. This interaction is implicated not
only in changes in phenylpropanoid metabolism, but also affects root hair cell
