Abstract: In process of the inter action between plants and microorganisms, microorganisms can take specific compound released by plants as chemical signal. The signal is soon effective on microorganisms. Therefore, the microorganism produce gene expression which is nece. ssary in order to attack host plants. Since Stachel (1985) first reported that acetosyringone and α-hydroxyace- tosyringone contained in percolating substance of wound cells in tobacco roots could activate toxic genes (vir), the conception, that signal molecules of the plant act as inducers of gene expression, has been suggested. Recent research advances on this field mentioned above have been summerized in present paper.

Key words: signal molecule, Inducer of gene expression