Molecular and physiological studies on oxidative burst and active defense mechanism in plant and its application for disease tolerance

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This project made it clear the followings on molecular mechanisms of oxidative burst (OXB) and active defense-network in Phytophtora infestans-infected potato plants. 1)In the course of the defense response, immediately-responsive OXB and induced OXB, which were dependent on superoxide-generating NADPH oxidase, RbohA and RbohB, were induced and then played a key signal role in the induction of HR-type defense response. 2)RbohA was activated through Ca^<2+> influx and a Ca^<2+>-dependent protein kinase, whereas RbohB was induced under control of MAPK cascade, and then activated by CDPK in relation to the 1st OXB. 3)A transient expression of MEK1^<DD> of MAPKK, that was modified by amino acid exchange to be constitutively active, caused activation of SIPK and WIPK of MAPK, induction of RbohB, HMGR,PVS etc. and then induction of HR-type defense response. 4)Activated MPK1 phosphorylated multiple host proteins (PPS1-8),PPS3 of which regulated expressions of RbohB, HMGR, and PVS. 5)Compatible races also induced activation of MAPK cascade and induction of non-active RbohB,HMGR and PVS, and stimulate infection-specific GUS expression in transgenic potato with PVS3 promoter-linked GUS gene. 6)NO generation was found to be accompanied by the 1st OXB, playing an important role in induction of HR-type response. 7)The NO generation was dependent on inducible-nitrate reductase (NR) and other unknown enzyme. 8)Local OXB stimulated a sequential Ca^<2+> influx among inner tissue cells, and this signal came to stimulate systemic OXB in the surface tissue, following expression of RbohB and PAL for induction of systemic acquired resistance (SAR). 9)Transgenic potato plants with PVS3 promoter-linked MEK^<DD> demonstrated tolerance to virulent P.infestans and Alternaria solani with HR-type defense response.