Biology Reference
In-Depth Information
Zmccr1 plants were undistinguishable from near isogenic lines. Since
ZmCCR1 is mutated in an intron, this result may be caused by some
residual activity of the mutated gene or/and gene redundancy. Using an
RNA interference-mediated silencing strategy, Tu and colleagues
dramatically decreased transcript level of CCR1 in perennial ryegrass,
L. perenne (
Louie et al., 2010; Tu et al., 2010
). In this study, lpccr1-1 plants
grown under field conditions showed up to 37% reduction in acetyl bro-
mide-soluble lignin, in comparison to control plants. The S/G ratio in
samples from field-grown lpccr1 showed no significant difference from
that of control plants. Interestingly, as suggested by transcriptomic analysis
in Zmccr1 mutants, flavonoid metabolisms was substantially deregulated.
Again as observed for Zmccr1 mutants, lpccr1 plants showed up to 13.6%
increase in digestibility without any obvious phenotypes in the field, indi-
cating that partially deficient CCR plants may be ideal crops for biofuel
or/and animal food production.
Lignin genes are hypothesized to be important players in plant defence. In
rice, a CCR allele, first identified as a unique locus named Snl6, showed up also
as a suppressor of the NH1-mediated lesion mimic phenotype (
Bart et al.,
2010
). NH1 is an ortholog of PR1 in rice. Overexpression of NH1 confers
resistance to bacterial pathogens and leads to spontaneous cell death pheno-
type. The authors showed that indeed, Snl6 disrupts the mediated constitutive
expression of PR genes, providing a mechanism for the role of NH1-mediated
resistance. Bart and colleagues also noted that phloroglucinol-HCl staining
was reduced in the leaves of Snl6 mutants as compared to WT plants further
suggesting a role of Snl6 in lignification. The authors associated this phenotype
with an increase of sugar release after hot water treatment. As previously
stated, Snl6 mutant lines do not display any obvious morphological phenotype
however, lignin content and quality were not analyzed in detail. Therefore the
need remains for further investigation to confirm a role of these CCR genes in
lignin biosynthesis. Nevertheless, a role of CCR in plant defence of rice was
previously supported by a study of
Kawasaki et al.(2006)
as CCR was
identified as an effector of a member of Rac/Rop family (
Kawasaki et al.,
2006
). These genes belong to the family of small GTPases that play a role in
defence. It remains unclear whether these CCR-like genes are truly involved in
lignin biosynthesis or involved in related phenolic compounds biosynthesis.
C. CAFFEIC ACID O-METHYLTRANSFERASE (COMT OR OMT1)
COMT catalyses the O-methylation on C5 position of 5-hydroxyconiferalde-
hyde/(coniferyl alcohol). COMTs may also O-methylate on C3 position
of caffeoyl-aldehyde/alcohol as suggested by previous studies (
Do et al., 2007
).
