Poster: Plant Pathogen/Symbiont Interactions

Abs # 713: Spermine induces a set of genes which have been identified as hypersensitive response genetic marker in tobacco leaves

Presenter:	Takahashi, Yoshihiro , ytaka@ige.tohoku.ac.jp
Authors	Takahashi, Yoshihiro  (A)   T, Berberich  (B)   A, Miyazaki  (A)   T, Kusano  (A)
Affiliations:	(A): Graduate School of Life Sciences, Tohoku Univ. (B): Botanisches Institut, Goethe-Universitaet

Plants are frequently exposed to various pathogens and incompatible host plants can tolerate pathogens by activating defense systems. The defense reaction associated with localized cell death is called hypersensitive response (HR), which prevents the further spread of pathogens from the invasion sites. The cell death in HR is known to share characteristics of mammalian apoptosis, a kind of the programmed cell death. Polyamines (PAs), putrescine, spermidine and spermine (Spm), are organic cations with low molecular weight that are implicated in various physiological and developmental processes in all organisms including plants. Whereas PAs are essential for growth, their excessive accumulation triggers apoptosis in various animal cells. A role of PAs in plant-microbe interactions was initially proposed by Greenland and Lewis (1984). They showed that PA levels were significantly altered by pathogen infection. Yamakawa et al (1998) reported that TMV-infected tobacco leaves carrying N gene contained higher levels of free Spm in the intercellular spaces than those of healthy leaves. They also showed that Spm induced PR genes and elicited resistance to TMV. The result suggested that Spm was another key molecule to transduce defense signal in TMV-infected HR and defense response in tobacco leaf. Here we isolated Spm-responsive genes from tobacco and identified hin1 gene which is a HR marker gene. Other PAs have no effect on hin1 induction. The induction was prevented by pretreatment with antioxidants and calcium channel blockers. We will also show the effect of Spm on expression of other HR marker genes. Our data suggest that Spm induces a set of HR marker genes, via a signal transduction pathway in which reactive oxygen species and calcium influx are involved.