MOLECULAR BREEDING OF DISEASE RESISTANT PLANTS WITH ARTIFICIAL CONTROL OF ACTIN RELATED GENE EXPRESSION

植物细胞可以通过快速和剧烈的细胞质重排来响应各种内部和外部刺激。这些变化通常是由动态细胞骨架、微管网络、肌动蛋白微丝及其相关蛋白介导的。由于植物自身不能移动，因此细胞骨架对细胞内部的时空控制是植物在多变环境下生存的必要条件。我们发现真菌侵染过程中微丝发生动态重组，并利用几种肌动蛋白抑制剂证明了肌动蛋白细胞骨架参与了真菌侵染的防御机制。这些结果揭示了抵抗机制的时空控制的重要性。此外，这一发现不仅为防御反应提供了新的前景，而且为改良作物的基因工程提供了新的推测来源。最近，已经知道Rho家族小的gtpase已经成为肌动蛋白细胞骨架的关键调节因子，并通过它们与多个靶蛋白的相互作用而出现。对植物Rac的功能知之甚少，但最近的研究表明，一些Rac亚型可能在花粉管顶端生长的细胞分裂和极化控制中起作用。这些结果使我们假设植物Rac gtpase可能参与了微丝的重组和对真菌入侵的防御反应的极化。为了验证这一假说，我们克隆了烟草Rac基因并在烟草植株中过表达。在Rac3基因过表达者中，PR1a基因自发表达，而亲本SR-1则诱导表达。在过表达者中，通过接种非病原体获得了对BTH的敏感性增加和PR1a基因的表达增强。另一方面，通过损伤，没有观察到PR1b的表达，自发的PR1a表达被抑制。这些结果表明Rac可能作为串扰调节剂同时调控防御信号转导中的水杨酸和茉莉酸途径。综上所述，我们认为Rac基因可能是抗病植物基因工程的目标。少

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 … More 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