Department of Biological Production, Faculty of Bioresource Sciences, Akita Prefectural University, 241-438 Kaidobata Nishi, Nakano-Aza, Shimoshinjo, Akita, 010-0195, Japan.
Planta. 2013 Oct;238(4):753-70. doi: 10.1007/s00425-013-1930-0. Epub 2013 Jul 20.
The oncogenic 6b gene of Agrobacterium tumefaciens induces a number of morphological and metabolic alterations in plants. Although molecular functions associated with the 6b genes have been proposed, including auxin transport, sugar transport, transcriptional regulation, and miRNA metabolism, so far an unequivocal conclusion has not been obtained. We investigated the association between auxin accumulation and tumor development of the tobacco seedlings expressing the AK-6b gene under the control of the dexamethasone-inducible promoter. Indole-3-acetic acid (IAA) localization was examined by immunochemical staining with monoclonal antibody against IAA and by histochemical analysis using the IAA-specific induced construct, DR5::GUS (β-glucuronidase). Both procedures indicated that IAA preferentially accumulated in the tumorous protrusions as well as in newly developing vascular bundles in the tumors. Furthermore, true leaves also showed abaxial IAA localization, leading to altered leaves in which the adaxial and abaxial identities were no longer evident. Co-localization of cytokinin and auxin in the abaxial tumors was verified by immunochemical staining with an antibody against cytokinin. Treatment of AK-6b-seedlings with N-1-naphthylphthalamic acid, an inhibitor of polar auxin transport, promoted the morphological severity of phenotypes, whereas 1-naphthoxyacetic acid, a specific auxin influx carrier inhibitor, induced tumor regression on cotyledons and new tumorous proliferations on hypocotyls. Prominent accumulation of both auxin and cytokinin was observed in both regressed and newly developing tumors. We suggest from these results that modulation of auxin/cytokinin localization as a result of AK-6b gene expression is responsible for the tumorous proliferation.
根癌农杆菌的致癌 6b 基因诱导植物发生许多形态和代谢变化。尽管已经提出了与 6b 基因相关的分子功能，包括生长素运输、糖运输、转录调控和 miRNA 代谢，但到目前为止，还没有得出明确的结论。我们研究了在 dexamethasone 诱导启动子控制下表达 AK-6b 基因的烟草幼苗中，生长素积累与肿瘤发育之间的关系。通过用针对 IAA 的单克隆抗体进行免疫化学染色和使用 IAA 特异性诱导构建体 DR5::GUS（β-葡萄糖醛酸酶）进行组织化学分析来检查 IAA 的定位。这两种方法都表明，IAA 优先在肿瘤突起以及肿瘤中新发育的血管束中积累。此外，真叶也表现出背面 IAA 定位，导致叶片发生变化，其中正面和背面的特征不再明显。通过用针对细胞分裂素的抗体进行免疫化学染色，验证了细胞分裂素和生长素在背面肿瘤中的共定位。用极性生长素运输抑制剂 N-1-萘基邻苯二甲酰胺处理 AK-6b 幼苗促进了表型的形态严重程度，而生长素内流载体抑制剂 1-萘氧基乙酸则诱导子叶上的肿瘤消退和下胚轴上新的肿瘤性增殖。在消退和新发育的肿瘤中都观察到生长素和细胞分裂素的明显积累。从这些结果中，我们认为 AK-6b 基因表达导致生长素/细胞分裂素定位的调节是肿瘤增殖的原因。
