| Budget Amount *help |
¥3,800,000 (Direct Cost: ¥3,800,000)
Fiscal Year 2000: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 1999: ¥3,000,000 (Direct Cost: ¥3,000,000)
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| Research Abstract |
Plant cells can respond to a variety of internal and external stimuli with rapid and dramatic rearrangements of their cytoplasm. These changes are often mediated by a dynamic cytoskeleton, the network of microtubules, actin microfilaments and their associated proteins. Because plants can't move themselves, quick responding capability taking from temporal and spatial control of cellular interior by the cytoskeleton must be essential to survive under changeable environment. We found the occurrence of dynamic reorganization of microfilaments during fungal invasion and evidenced the involvement of actin cytoskeleton in defense mechanism against fungal invasion, using several actin inhibitors. These results revealed the importance of temporal and spatial control of resistance machinery. Furthermore, the finding doesn't provide only new prospect of defense responses, but also new putative source of genetic engineering for improving crop plant. Recently, it has been known that Rho family smal
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l GTPases have emerged as key regulators of the actin cytoskeleton and, through their interaction with multiple target proteins. Little is known about Plant Rac function, but recent works suggest that some Rac isoforms may play a role in controlling cell division and polarization in tip growing pollen tubes. These results lead us to the hypothesis that plant Rac GTPases may be involved in reorganization of microfilaments and polarization of defense responses against fungal invasion. To investigate this hypothesis, we cloned tobacco Rac genes and overexpressed in tobacco plants. In Rac3 gene overexpressors, PR1a gene expressed spontaneously, whereas inducible expression was observed in the parent, SR-1. Increased sensitivity to BTH and enhanced expression of PR1a gene by inoculation of a nonpathogen was obtained in overexpressors. On the other hand, by wounding, no expression of PR1b was observed and spontaneous PR1a expression was suppressed. These results suggest that Rac may regulate both salicylate and jasmonate pathway in a defense signal transduction as a cross-talk regulator. Together all, we concluded that Rac genes are possible target for the genetic engeeniring of disease resistant plant. Less
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