Regulation of the chitinase gene expression in suspension-cultured rice cells by N-acetylchitooligosaccharides: differences in the signal transduction pathways leading to the activation of elicitor-responsive genes

Expression patterns of chitinase transcripts induced by N-acetylchitooligos accharide elicitor were analyzed by northern blot hybridization in order to reveal a signal transduction pathway leading to the activation of class I chitinase genes (Cht-1 and Cht-3), which may play an important role in prod ucing N-acetylchitooligosaccharide elicitor. The transcription level of bot h genes was enhanced in response to N-acetylchitooligosaccharides larger th an pentaose at subnanomolar concentrations. These structure and dose depend encies were consistent not only with those for a 75 kDa high-affinity bindi ng protein for N-acetylchitooligosaccharide elicitor in the plasma membrane , but also with other series of cellular responses including phytoalexin pr oduction and the expression of elicitor-responsive genes (EL2, EL3). Theref ore, the elicitor signal to evoke these cellular responses including the ac tivation of the chitinase genes could be common and transmitted into cells through the 75 kDa protein. However, the signal transduction pathway for th e activation of the chitinase gene appeared to diverge from those for the o ther elicitor-responsive genes shortly after the signal perception. It was shown that the induction of chitinase expression by N-acetylchitooligosacch aride would require protein phosphorylation, but not de novo protein synthe sis. The oxidative burst was demonstrated not to be necessary for transcrip tional induction of the all four elicitor-responsive genes (Cht, PAL, EL2, EL3) by N-acetylchitooligosaccharide.