Agriculture Reference
In-Depth Information
Control of Glucosinolate Biosynthesis - MYB Transcription
Factors
Glucosinolate biosynthesis is highly regulated by a network of transcription factors
in response to biotic and abiotic stress (Gigolashvili et al.
2007
,
2008
; Sønderby
et al.
2007
). They belong to two groups of the R2R3-MYB family of transcription
factors. The first group consists of three members: MYB28, MYB76 and MYB29,
and is involved in the control of aliphatic glucosinolate biosynthesis (Gigolashvili
et al.
2008
). The second group is responsible for control of biosynthesis of indolic
glucosinolates and includes MYB51, MYB122, and MYB34 (Gigolashvili
et al.
2007
). Glucosinolates controlled by members of these two groups can be
alternatively called high aliphatic glucosinolates (1-3) and high indolic
glucosinolates (1-3), respectively (Fig.
3.5
). T-DNA insertions, RNAi or over-
expression of these factors affects the expression of glucosinolate biosynthesis
genes and the level of glucosinolates. MYB34, MYB51 and MYB122 have differ-
ent functions in the regulation of the pathway (Gigolashvili et al.
2007
). Although
all of them up-regulate the genes from the biosynthesis pathway, MYB34 and
MYB122 also function as stimulators of auxin biosynthesis, whereas MYB51
additionally activates the glucosinolate biosynthesis pathway (Gigolashvili
et al.
2007
). Studies on MYB28, MYB29 and MYB 76 showed that they are able
to transactivate each other in control of biosynthesis of aliphatic glucosinolates.
They also downregulate the expression of enzymes involved in the synthesis of
indolic glucosinolates (Gigolashvili et al.
2008
). Analysis of MYB28 and MYB29
revealed that MYB28 is essential for the synthesis of aliphatic glucosinolates
whereas MYB29 induces biosynthetic genes in response to plant hormone methyl
jasmonate (Hirai et al.
2007
). Maruyama-Nakashita and co-workers (
2006
) showed
that mutation of SLIM1 additionally affects the expression of MYB34, suggesting
that this factor may be negatively controlled by SLIM1 in response to sulfur
deficiency. There is some evidence that SLIM1 also might affect the expression
of MYB28 and MYB29, however the effect is not completely clear (Hirai
et al.
2007
). More recently, it was suggested that MYB factors are not only involved
in the regulation of the glucosinolate biosynthesis genes, but also other genes in the
sulfur reduction pathway. Yatusevich et al. (
2010
) concluded that
APR1
and
APR3
are under control of all MYB factors whereas
APR2
is regulated by only some of
them. They suggested also that
APK1
and
APK2
are a part of the glucosinolate
synthesis network controlled by MYB factors, whereas
APK3
and
APK4
have much
lower input to the network. Glucosinolate biosynthesis may be also regulated by the
DNA-binding-with-one-finger (DOF) transcription factor, OBP2, which is induced
by herbivory and methyl jasmonate (Skirycz et al.
2006
). Additionally, changes in
expression of calmodulin binding IQD protein cause the variation in glucosinolate
composition (Levy et al.
2005
).
