Molecular Mechanism of Crwon Gall Tumor Formation (Transfer of T-DNA into Monocotyledonous plants)

携带Ti质粒的根癌农杆菌在多种双子叶植物上诱发冠瘿瘤。在感染植物后，Ti质粒的T-DNA通过未知机制转移到植物细胞中并整合到植物核DNA中。T-DNA的转移需要存在于Ti质粒中的毒力（vir）基因。大多数vir基因响应于诸如乙酰丁香酮和木质素前体的植物信号分子而表达。我们以前的研究结果表明，这样的信号分子存在于单子叶植物中，除了双子叶植物之外，被认为对农杆菌具有抗性的植物也存在。在这些单子叶植物诱导剂的纯化过程中，我们发现从单子叶植物幼苗匀浆中提取的某些物质能显著增强信号分子对vir的诱导作用。增强物质是单糖或其衍生物的确凿证据。我们研究了商业上可获得的糖是否增强vir诱导。结果表明，一组醛糖（D-葡萄糖，D-半乳糖，L-阿拉伯糖和D-木糖），是已知的主要细胞壁单糖的前体，提高vir诱导超过10倍。同样，2-脱氧-D-葡萄糖，一种非代谢糖，也是有效的。当删除引入到VirA蛋白的周质区的编码区，增强有效糖消失，但在这个突变体中的信号分子诱导vir表达。这些结果表明，这些糖直接加速由诱导剂引发的信号传导过程，这导致vir基因表达的增加。

Agrobacterium tumefaciens harboring the Ti Plasmid incites crown gall Tumor on a wide variety of dicotyledonous plants. Upon infection of plants, T-DNA of the Ti plasmid is transferred by unknown mechanisms to plant cells and integrated into plant nuclear DNA. The transfer of T-DNA requires virulence (vir) genes which are present in the Ti plasmid. Most vir genes are expressed in response to such plant signal molecules as acetosyringone and lignin precursors. Our previous results showed that such signal molecules are present in monocotyledonous plants plants which are thought to be resistant to Agrobacterium in addition to dicotyledonous. During purification of these monocotyledonous inducers, we found that some substance extracted from homogeneities of monocotyledonous seedlings markedly enhanced vir induction by signal molecules. Ciroumstantial evidence that the enhancing substances are monosaccharides or their derivatives. We examined whether or not commercially available sugars enhance vir induction. The results show that a group of aldoses (D-glucose, D-galactose, L-arabinose and D-xylose) that are known precursors of major cell wall monosaccharides, enhances vir induction wre than 10-fold. Likewise, 2-deoxy-D-glucose, a normetabolized sugar, is also effective. When a deletion was introduced into the coding region of the periplasmic region of VirA protein, enhancement by effective sugars disappeared, but vir expression was induced by the signal molecules in this mutant. These results suggest that these sugars directly accelerate a signaling process initiated by the inducers, which results in increase in increase in expression of the vir genes.