Biology Reference
In-Depth Information
C. STEM LACCASES: FIRST IN VIVO EVIDENCE IMPLICATING
LACCASES IN LIGNIN POLYMERIZATION
Among the 17 arabidopsis laccases, six are expressed in the inflorescence stem.
Homozygous T-DNA insertion lines for the six genes were obtained and lignin
contents of mature stems determined (
Table III
). Only mutants of the AtLAC4
(lac4-1 and -2) and AtLAC17 (lac17) genes, which are the main laccases
expressed in stems, had an approximately 10% decreased lignin content when
compared to the WT (
Berthet et al.,2011
). These lines showed no growth
phenotype when plants were grown in greenhouse conditions. Aweak irregular
xylem phenotype similar to that observed for irx12 (
Brown et al.,2005
)was
reported for lac4-1andlac4-2 mutants grown under continuous light condi-
tions. As AtLAC4 and AtLAC17 are both tightly coexpressed and homologous
genes (
Fig. 1
A and B), they could display some functional redundancy. This
hypothesis prompted us to produce double homozygous T-DNA insertion lines
(lac4-1 lac17 and lac4-2 lac17). These two double mutants displayed an impor-
tant reduction (between 19% and 39%) in lignin content in their mature stems
when compared to the WT (
Berthet et al.,2011
). This reduced lignin level was
associated with an irregular xylem phenotype characteristic of secondary cell
wall deficient mutants (
Brown et al.,2005
). Alteration of lignin structure
(higher S/G ratio) was also observed in these lines, suggesting a higher impact
on G-lignin deposition. This result was found to be consistent with the hypoth-
esis that laccases would be involved in the early stages of lignification (
Bao
et al., 1993; Donaldson, 2001
). AtLAC17 was mainly expressed in interfasci-
cular fibres, whereas AtLAC4 was expressed in both xylem and interfascicular
fibres. According to the literature (
Gavnholt and Larsen, 2002; Lewis and
Yamamoto, 1990
), to assess that an oxidase plays a role in lignin polymeriza-
tion requires the fulfilment of the three following criteria: (1) a spatial and
PtrLAC17: POPTR_0007s13050; PtrLAC18: POPTR_0008s06430; PtrLAC19:
POPTR_0008s07370; PtrLAC20: POPTR_0008s07380; PtrLAC21: POPTR_
0009s03940; PtrLAC22: POPTR_0009s04720; PtrLAC23: POPTR_0009s10550;
PtrLAC24: POPTR_0009s15840; PtrLAC25: POPTR_0009s15860; PtrLAC26:
POPTR_0010s19080; PtrLAC27: POPTR_0010s19090; PtrLAC28: POPTR_
0010s20050; PtrLAC29: POPTR_0011s06880; PtrLAC30: POPTR_0011s12090;
PtrLAC31: POPTR_0011s12100; PtrLAC32: POPTR_0012s04620; PtrLAC33:
POPTR_0013s14890; PtrLAC34: POPTR_0014s09610; PtrLAC35: POPTR_
0015s04330; PtrLAC36: POPTR_0015s04340; PtrLAC37: POPTR_0015s04350;
PtrLAC38: POPTR_0015s04370; PtrLAC39: POPTR_0016s11500; PtrLAC40:
POPTR_0016s11520; PtrLAC41: POPTR_0016s11540; PtrLAC42: POPTR_
0016s11950; PtrLAC43: POPTR_0019s11810; PtrLAC44: POPTR_0019s11820;
PtrLAC45: POPTR_0019s11830; PtrLAC46: POPTR_0019s11850; PtrLAC47:
POPTR_0019s11860; PtrLAC48: POPTR_0019s14530; PtrLAC49: POPTR_
0091s00270; PtrLAC50: POPTR_0958s00200.
