Sakamoto T, Nishimura A, Tamaoki M, Kuba M, Tanaka H, Iwahori S, Matsuoka M
Institute of Agriculture and Forestry, University of Tsukuba, Tsukuba, Ibaraki 305-0006, Japan.
Plant Cell. 1999 Aug;11(8):1419-32. doi: 10.1105/tpc.11.8.1419.
Overproduction of the tobacco KNOTTED1-type homeodomain proteins NTH1, NTH15, and NTH23 in transgenic tobacco plants causes mild, severe, and no morphological alterations, respectively. The deduced amino acid sequences of the homeodomains and adjacent ELK domains are highly conserved, and the N-terminal KNOX domains also are moderately conserved. To investigate the contributions of both the conserved and divergent regions to the severity of morphological alterations, we generated chimeric proteins by exchanging different regions of NTH1, NTH15, and NTH23. The severity of the abnormal phenotype was dependent upon the synergistic action of both the N terminus, containing the KNOX domain, and the C terminus, containing the ELK homeodomain. Detailed analysis focusing on the C terminus revealed that the C-terminal half of the ELK domain is more effective in inducing the abnormal phenotypes than are the homeodomains. For the N terminus, severe morphological alterations were induced by exchanging a part of the KNOX domain of NTH1 with the corresponding region of NTH15. This limited region in the KNOX domain of all homeodomain proteins includes a predicted alpha-helical region, but only that in NTH15 is predicted to form a typical amphipathic structure. We discuss the possibility, based on these results, that the secondary structure of the KNOX domain is important for the induction of abnormal morphology in transgenic tobacco plants.
在转基因烟草植株中，烟草KNOTTED1类同源异型域蛋白NTH1、NTH15和NTH23的过量表达分别导致了轻微、严重和无形态学改变的情况。同源异型域和相邻ELK域的推导氨基酸序列高度保守，N端KNOX域也有适度保守。为了研究保守区和差异区对形态学改变严重程度的作用，我们通过交换NTH1、NTH15和NTH23的不同区域生成了嵌合蛋白。异常表型的严重程度取决于包含KNOX域的N端和包含ELK同源异型域的C端的协同作用。对C端的详细分析表明，ELK域的C端一半在诱导异常表型方面比同源异型域更有效。对于N端，通过将NTH1的部分KNOX域与NTH15的相应区域交换诱导了严重的形态学改变。所有同源异型域蛋白的KNOX域中的这个有限区域包含一个预测的α螺旋区域，但只有NTH15中的该区域预测形成典型的两亲结构。基于这些结果，我们讨论了KNOX域的二级结构对转基因烟草植株异常形态诱导很重要的可能性。
