Long-term Exposure to Methyl Jasmonate Increases Myrosinases TGG1 and
TGG2 in Arabidopsis coi1 and myc2,3,4 Mutants
Abstract
Myrosinase is an enzyme that activates a group of metabolites, namely
glucosinolates, which are involved in the defense against herbivores and
pathogens. In Arabidopsis thaliana, THIOGLUCOSIDE GLUCOHYDROLASE
1 (TGG1) and TGG2 are two myrosinases that accumulate in specialized
myrosin cells of rosette leaves. Here, we show that prolonged exposure
to the wounding hormone methyl jasmonate (MeJA) enhances TGG1 and
TGG2 expression independent of the canonical jasmonic acid (JA)
signaling pathway. We found that airborne MeJA treatment for up to
5-days enhanced both TGG1 and TGG2 gene expression and
their protein levels in Arabidopsis leaves. TGG1 and TGG2
gene expression did not stop in two JA signaling pathway mutants, namely
coi1-16 and myc2,3,4, after 5-days of MeJA treatment,
although other typical JA responses were completely stopped in these two
mutants. FAMA is a transcription factor that participates in the
specification of myrosin cell development, but it does not appear to be
involved in TGG1 and TGG2 gene expression regulation in
the 5-day MeJA treatment, as its expression did not increase. Taken
together, our results suggest the existence of an alternative JA
signaling pathway that is activated by long-term exposure to MeJA.