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

携带钛质粒的根癌农杆菌可在多种双子叶植物上诱发冠瘤。在侵染植物后，T-DNA以未知的机制转移到植物细胞中，并整合到植物的核DNA中。T-DNA的转移需要存在于钛质粒中的毒力(VIR)基因。大多数VIR基因是在乙酰丁香酮和木质素前体等植物信号分子的作用下表达的。我们以前的结果表明，这种信号分子存在于单子叶植物中，这些植物除了双子叶植物外，还被认为对农杆菌具有抗性。在这些单子叶诱导剂的纯化过程中，我们发现从单子叶幼苗匀浆中提取的一些物质显著增强了信号分子对VIR的诱导。增强物质是单糖或其衍生物的证据。我们研究了市场上可获得的糖是否增强了VIR的诱导。结果表明，已知的主要细胞壁单糖前体D-葡萄糖、D-半乳糖、L-阿拉伯糖和D-木糖可使VIR的诱导增强10倍以上。同样，2-脱氧-D-葡萄糖，一种非代谢糖，也是有效的。当在VirA蛋白的周质区域的编码区引入缺失时，有效糖的增强作用消失，但VIR的表达被该突变体中的信号分子诱导。这些结果表明，这些糖直接加速了由诱导剂启动的信号传递过程，从而导致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.