MYB-related transcription factor NtMYB2 induced by wounding and elicitors is a regulator of the tobacco retrotransposon Tto1 and defense-related genes

Transposition of the tobacco retrotransposon Tto1 is regulated mainly by transcription from the long terminal repeat (LTR). Functional analysis of the LTR showed that the 13-bp motif is a cis-regulatory element involved in activation by tissue culture, wounding, and treatment with elicitors. The 13-bp motif contains a conserved motif (L box) that has been implicated in the expression of phenylpropanoid synthetic genes in response to defense-related stresses. To gain further insight into the regulatory mechanism of the retrotransposon and defense-related genes, cDNAs encoding four different proteins binding to the 13-bp motif have been isolated and characterized. One protein is identical to the previously reported NtMYB1, the RNA for which is induced by virus infection; the others are also MYB-related factors. One of these factors, NtMYB2, was analyzed in detail. NtMYB2 mRNA was induced by wounding and by treatment with elicitors. NtMYB2 activated expression from the promoter with the 13-bp motif and from the promoter of the phenylalanine ammonia lyase gene (Pv-PAL2) in tobacco protoplasts. Overexpression of NtMYB2 cDNA in transgenic tobacco plants induced expression of Tto1 and a PAL gene. Together, these results indicate that NtMYB2 is involved in the stress response of the retrotransposon and defense-related genes.