Biology Reference
In-Depth Information
zipper TF, REVOLUTA/INTERFASCICULAR FIBERLESS1 (REV/
IFL1), was shown to interfere with auxin transport and result in the loss of
secondary thickening in interfascicular fibres (
Zhong and Ye, 2001
). Increas-
ing evidence indicates that most major hormones affect the lignin biosyn-
thetic pathway and the expression of some TF involved in lignin biosynthesis
has been shown to be modulated by plant hormone application. In aspen,
indole-3-acetic acid (IAA) and gibberellic acid (GA) induced the expression
of the lignin repressor PttMYB21a, while cytokinin repressed its expression
(
Karpinska et al., 2004
). Moreover, AtMYB32 negatively regulates lignin
biosynthesis in Arabidopsis and its expression during lateral root formation is
highly induced by auxin application (
Preston et al., 2004
).
Expression of another MYB TF, AtMYB52 was enhanced in an ABA-
hypersensitive Arabidopsis mutant (ahs1) and AtMYB52 overexpression lines
confer ABA hypersensitivity during postgermination growth (
Park et al.,
2011
). Transgenics overexpressing AtMYB52 were drought tolerant and
their seedlings were salt sensitive. Further analyses showed that expression
levels of a number of genes involved in ABA response and cell wall biosyn-
thesis also occurred (
Park et al., 2011
). Another example linking ABA
signalling to SW formation and lignification is the ABA-responsive TF
VNI2, a SW repressor which integrates ABA-mediated high salinity stress
signals into leaf ageing (
Yang et al., 2011
).
In an in silico survey of gene expression that we performed using Gene-
vestigator V3 (
Hruz et al., 2008
), we did not identify any significant changes
in the transcript accumulation of the lignin-specific TF AtMYB58,
AtMYB63 and AtMYB85 in the response of seedlings to most exogenous
hormones applied such as IAA, GA, 1-aminocyclopropane-1-carboxylic acid
(ACC), zeatin, ABA, BRs, and salicylic acid (SA). Only a slight induction
was observed in the case of methyl jasmonate (MeJA) application. Similar
findings were observed when examining the upstream TF AtMYB46, NST1,
NST2 and NST3. On the other hand, the application of brassinolide with
boric acid to Arabidopsis cell cultures induced in vitro treachery element
formation (
Kubo et al., 2005
) accompanied by high expression of
AtMYB46, AtMYB58, AtMYB63 and AtMYB85. Indeed, the regulation of
SW TF by hormones is likely to be tissue-/cell-type dependent, and whether
or not hormones regulate lignin TF in organs and tissues with high lignin
content still remains to be determined. It would also be relevant to examine
SW TF expression in hormone-deficient mutants.
Interestingly, reduced lignin content in plants affects hormone homeosta-
sis and/or signalling. Selective lignin downregulation leads to constitutive
defence response expression in alfalfa (Medicago sativa)(
Gallego-Giraldo
et al., 2011
) and the stress hormone SA was found to be inversely
