Biology Reference
In-Depth Information
plants. The gene altered in the bm2 mutation is not yet identified and
different hypotheses are considered (
Barri`re et al., 2004a; Vermerris and
Boon, 2001
). Based on the current knowledge, the bm2 mutation could affect
coniferyl alcohol transport or/and glycosylation. The bm4 mutant is the least
known of the four original bm mutants. A slightly lower lignin content and a
reduced frequency of
-O-4-linked G units was shown in bm4 as in bm2
plants, without incorporation of unusual compounds in lignins (
Barri`re
et al., 2004a; Vermerris et al., 2010
). The gene underlying the bm4 mutation
is also unknown. No data have been yet published related to the lignin and
cell wall traits in bm5, bm6 and bm7. Preliminary results indicate a lower
lignin content and a higher cell wall degradability of both bm5 and bm6
plants (M
´
chin and Barri
`
re, unpublished data, no data available for bm7).
b
V. QTL AND BREEDING
Lignification and cell wall degradability trait QTL (Quantitative Trait Loci)
are available from a few maize RIL (Recombinant Inbred Line) progenies
specifically developed for such investigations (
Barri`re et al., 2008, 2010;
L¨bberstedt et al., 1997; M´chin et al., 2001; Riboulet et al., 2008; Roussel
et al., 2002
), but lignin trait data are also available from corn borer tolerance
studies (
Bohn et al., 2000; Cardinal et al., 2003; Krakowsky et al., 2003, 2004,
2005; Papst et al., 2001
). Based on a metaQTL analysis, nearly 40 and 25
metaQTL locations for lignin-related traits and cell wall degradability, re-
spectively, were identified in the maize genome (
Truntzler et al., 2010
).
Considering QTL colocalizations and their LOD values, hot spots were
shown in bins 1.05, 1.07, 4.08, 5.04 and 6.05/06, 10.03/04. QTL for in vitro
neutral detergent fibre digestibility (IVNDFD QTL) and acid detergent
lignin (ADL) content appeared to be colocalizing in nearly 70% of occur-
rences, but 40% of ADL/NDF content QTL do not colocalized with
IVNDFD QTL. In most cases, KL/NDF QTL did not colocalized with cell
wall degradability QTL, indicating that in grasses, only the acido-resistant
part of lignin has a significant inhibitory effect on cell wall susceptibility to
enzymatic degradation. Variations in lignin structure, in acylation of S units
by pCA, and cross-linkages between arabinoxylan chains and G units of
lignins, or between arabinoxylan chains, likely explain the part of cell wall
degradability variations not explained by lignin content variations. Fifteen
QTL explaining at least 20% of the observed genetic variation for these
traits were observed in two progenies, including QTL for G and S content,
QTL for FA ethers and QTL for diferulates (diFA) (namely, 5-5diFA and
8-O-4diFA).
