Yoshida Kazuko, Iwasaka Rieko, Kaneko Takakazu, Sato Shusei, Tabata Satoshi, Sakuta Masaaki
Department of Biology, Ochanomizu University, Tokyo 112-8610 Japan.
Plant Cell Physiol. 2008 Feb;49(2):157-69. doi: 10.1093/pcp/pcn009. Epub 2008 Jan 16.
Leguminous plants have many paralogous genes encoding enzymes involved in the flavonoid biosynthetic pathway. Duplicate genes are predicted to contribute to the production of various flavonoid compounds and to have resulted in a diversity of legume species. We identified gene duplication in the transcription factors regulating flavonoid biosynthesis in the model legume Lotus japonicus. Three copies of a homolog of Arabidopsis thaliana TRANSPARENT TESTA2 (TT2), which is a MYB transcription factor that regulates proanthocyanidin biosynthesis, were present in the L. japonicus genome. The organ specificity and stress responsiveness differed among the three LjTT2s, and correlations between proanthocyanidin accumulation and the expression levels of LjTT2s were observed during seedling development. Moreover, three LjTT2s functionally complemented TT2 in transient expression experiments in A. thaliana leaf cells. The different reporter activity caused by LjTT2a was consistent with the affinity of physical interactions with TT8 and TTG1 in yeast two-hybrid experiments as well as the branching pattern of the phylogenetic tree. These results suggest that LjTT2 factors have diverse functions in the tissues in which they are expressed; in particular, LjTT2a is predicted to have evolved flexibility in interaction with other transcription regulators to resist environmental stresses.
豆科植物有许多旁系同源基因，这些基因编码参与类黄酮生物合成途径的酶。预计重复基因有助于各种类黄酮化合物的产生，并导致了豆科物种的多样性。我们在模式豆科植物百脉根中鉴定了调控类黄酮生物合成的转录因子中的基因重复现象。拟南芥透明种皮2（TT2）的一个同源物有三个拷贝，TT2是一个调控原花青素生物合成的MYB转录因子，存在于百脉根基因组中。三个LjTT2之间的器官特异性和胁迫反应性有所不同，并且在幼苗发育过程中观察到原花青素积累与LjTT2表达水平之间的相关性。此外，在拟南芥叶细胞的瞬时表达实验中，三个LjTT2在功能上互补了TT2。LjTT2a引起的不同报告基因活性与酵母双杂交实验中与TT8和TTG1的物理相互作用亲和力以及系统发育树的分支模式一致。这些结果表明，LjTT2因子在其表达的组织中具有多种功能；特别是，预计LjTT2a在与其他转录调节因子相互作用以抵抗环境胁迫方面具有进化的灵活性。
