Abstract:
Jasmonates (JA) are important regulators of plant defense responses that activate expression of many
wound-induced genes including the tomato proteinase inhibitor II (pin2) and leucine aminopeptidase (LAP)
genes. Elements required for JA induction of the LAP gene are all present in the −317 to −78 proximal
promoter region. Using yeast one-hybrid screening, we have identified the bHLH-leu zipper JAMYC2 and
JAMYC10 proteins, specifically recognizing a T/G-box AACGTG motif in this promoter fragment. Mutation
of the G-box element decreases JA-responsive LAP promoter expression. Expression of JAMYC2 and JAMYC10
is induced by JA, with a kinetics that precedes that of the LAP or pin2 transcripts. JAMYC overexpression
enhanced JA-induced expression of these defense genes in potato, but did not result in constitutive transcript
accumulation. Using footprinting assays, an additional protected element was identified, located directly
adjacent to the T/G-box motif. Mutation of this element abolishes JA response, showing that recognition of
this duplicated element is also required for gene expression. Knockout mutants in the AtMYC2 homolog gene
of Arabidopsis are insensitive to JA and exhibit a decreased activation of the JA-responsive genes AtVSP and
JR1. Activation of the PDF1.2 and b-CHI, ethylene/JA-responsive genes, is, however, increased in these
mutants. These results show that the JAMYC/AtMYC2 transcription factors function as members of a
MYC-based regulatory system conserved in dicotyledonous plants with a key role in JA-induced defense gene
activation
