Biology Reference
In-Depth Information
between the two functions, but these, as all other transporters involved in lignin
biosynthesis, remain enigmatic.
2. More than 'just' lignin
All CYP98A family members characterized biochemically to date were shown
to catalyse the 3-hydroxylation of phenylpropanoid moieties. But unlike C4H,
these 3-hydroxylases have a less stringent substrate specificity and can accept
multiple 4-coumaroyl-conjugates. The products, caffeoyl-conjugates and deri-
vatives thereof such as feruloyl- or sinapoyl-conjugates, are typical specialized
plant natural products that come in hundreds of varieties and accumulate in
a species-specific manner. Chlorogenic acid, that is caffeoyl-quinate, and
rosmarinic acid, that is caffeoyl-3,4-dihydroxyphenyllactate, are just two com-
mon examples (
Petersen et al.,2009
). Most CYP98A family members char-
acterized to date have a substrate preference for 4-coumaroyl-shikimate but
can also metabolize the quinate ester to appreciable levels, thus producing
chlorogenic acid. This holds true for the Arabidopsis CYP98A3 (albeit Arabi-
dopsis is not known to be able to produce chlorogenic acid in vivo), and also
for CYP98As from wheat (Triticum aestivum), globe artichoke (Cynara car-
dunculus), sweet basil (Ocimum basilicum), and coffee (Coffea canephora)
(
Gang et al., 2002; Mahesh et al., 2007; Moglia et al., 2009; Morant et al.,
2007
). Both coffee isoforms, CYP98A35 and CYP98A36, metabolized
p-coumaroyl shikimate at similar rates, but only CYP98A35 hydroxylates
the chlorogenic acid precursor p-coumaroyl quinate with the same efficiency
as the shikimate ester, indicting functional divergence within the gene family
(
Mahesh et al.,2007
). The sweet basil enzyme was also shown to be able to
hydroxylate the phenolic moiety of the rosmarinic acid precursor, albeit at a
very low rate (
Gang et al.,2002
). Likewise, another C3
0
H (CYP98A6) from a
different rosmarinic acid producing plant, Lithospermum erythrorhizon,
also catalyses the 3-hydroxylation of 4-coumaroyl-4
0
-hydroxyphenyllactic
acid and was therefore implicated in rosmarinic acid biosynthesis (
Matsuno
et al.,2002
), but other substrates were not tested. Coleus blumei also accumu-
lates large amounts of rosmarinic acid and the corresponding CYP98A14
from this species catalyses both the 3-hydroxylation of 4-coumaroyl-3
0
,4
0
-
dihydroxyphenyllactate and the 3
0
-hydroxylation of caffeoyl-4
0
-hydroxyphe-
nyllactate, in both cases forming rosmarinic acid. This was the first example of
a CYP98A that has no activity with 4-coumaroyl-shikimate or -quinate (
Eberle
et al.,2009
). Likewise, the two other CYP98Amembers present inArabidopsis,
CYP98A8 and A9, lack 4-coumaroyl-shikimate/quinate 3
0
-hydroxylase activi-
ty. They were shown to have evolved recently through retroposition fromC3
0
H
and have gained a novel function, that is, hydroxycinnamoyl-spermidine 3- and
5-hydroxylations involved in pollen development (
Matsuno et al.,2009
). In this
