Biology Reference
In-Depth Information
accumulation of aldehydes and a reduced lignin content to about 25% of WT
levels. Interestingly, normal lignin content and composition were recovered
when the WT CAD allele was overexpressed in one of the CAD-deficient
mutants (Bouvier d'Yvoire et al., in preparation).
Steps putatively carried out by PAL or/and TAL (eight genes in Brachypo-
dium and nine genes in maize), cinnamate 4-hydroxylase (three paralogs of
C4H in Brachypodium and four paralogs in maize), coumarate-3-hydroxylase
(one unique gene C3H in Brachypodium and two genes in maize), hydroxy-
cinnamoyl-CoA shikimate/quinate hydroxycinnamoyl transferase (two HCT
genes in Brachypodium and maize), caffeoyl coenzyme A 3-OMT (seven
CCoAOMT genes in Brachypodium and five genes in maize) and ferulate-5-
hydroxylase (four F5H in Brachypodium and two genes in maize) remain
elusive in grasses. Therefore, there the need remains for further investigation
into this area of plant biology.
IV. BROWN-MIDRIB MUTANTS WITH
UNKNOWN LOCI
The maize bm phenotype corresponds to mutant plants exhibiting a reddish-
brown pigmentation, associated with lignified tissues, of the leaf midrib and
stalk pith. Between 1922 and 1947, four non-allelic bm genes were described
(bm1-bm4), all segregating as simple Mendelian recessive traits. Based on
genetic investigations, bm1, bm2, bm3 and bm4 mutations were assigned to
maize bins 5.04, 1.11, 4.05 and 9.08, respectively (MaizeGDB,
www.
maizegdb.org
). No new maize bm mutations were described or investigated
during the nearly 60 years after the description of bm4 in 1947. A renewed
interest in bm mutations occurred with the characterization of the three bm
mutants, bm5, bm6 and bm7 (
Ali et al., 2010; Haney et al., 2008
), based on
allele testing of the 13 bm mutants which were available in the Maize Stock
Center (out of which two mutants with large growth defects were discarded).
Three mutants were identified as bm1, and three other as bm2, bm3 and bm4,
respectively, and the five other corresponded to the three new bm mutations.
Noteworthy, the latter mutations have yet to be mapped.
In bm2 mutants, reduced lignin content in addition to a significant reduc-
tion in the number of
b
-O-4-linked G units, without changes in the frequency
of
-O-4-linked S units, was observed. Also these mutants displayed a
slightly higher cell wall degradability (
Barri`re et al., 2004a
). Thioacidolysis
of bm2 lignins did not reveal any incorporation of unusual units, in contrast
to bm3 and bm1 lignins. A slight shift in pCA and FA ester levels and a
significant decrease in FA ether levels were also observed in mature bm2
b
