Kitamura Satoshi, Shikazono Naoya, Tanaka Atsushi
Department of Ion-Beam-Applied Biology, Japan Atomic Energy Research Institute, 1233 Watanuki-machi, Takasaki, Gunma 370-1292, Japan.
Plant J. 2004 Jan;37(1):104-14. doi: 10.1046/j.1365-313x.2003.01943.x.
Flavonoid compounds such as anthocyanins and proanthocyanidins (PAs; so-called condensed tannins) have a multitude of functions in plants. They must be transported from the site of synthesis in the cytosol to their final destination, the vacuoles. Three models have been proposed for sequestering anthocyanins in vacuoles, but the transport machinery for PAs is poorly understood. Novel Arabidopsis mutants, transparent testa 19 (tt19), which were induced by ion beam irradiation, showed a great reduction of anthocyanin pigments in the vegetative parts as well as brown pigments in the seed coat. The TT19 gene was isolated by chromosome walking and a candidate gene approach, and was shown to be a member of the Arabidopsis glutathione S-transferase (GST) gene family. Heterologous expression of a putative ortholog, petunia anthocyanin 9 (AN9), in tt19 complemented the anthocyanin accumulation but not the brown pigmentation in the seed coat. This suggests that the TT19 gene is required for vacuolar uptake of anthocyanins into vacuoles, but that it has also a function different from that of AN9. The depositional pattern of PA precursors in the mutant was different from that in the wild type. These results indicate that TT19 participates in the PA pathway as well as the anthocyanin pathway of Arabidopsis. As involvement of GST in the PA pathway was previously considered unlikely, the function of TT19 in the PA pathway is also discussed in the context of the putative transporter for PA precursors.
类黄酮化合物，如花色苷和原花青素（PAs；即所谓的缩合单宁）在植物中具有多种功能。它们必须从胞质溶胶中的合成部位运输到最终目的地——液泡。已经提出了三种将花色苷隔离在液泡中的模型，但对于PAs的运输机制了解甚少。通过离子束辐照诱导产生的新型拟南芥突变体——透明种皮19（tt19），其营养器官中的花色苷色素以及种皮中的褐色色素大幅减少。通过染色体步移和候选基因方法分离出了TT19基因，结果表明它是拟南芥谷胱甘肽S-转移酶（GST）基因家族的成员。在tt19中异源表达推定的直系同源基因矮牵牛花色苷9（AN9），可补充花色苷的积累，但不能补充种皮中的褐色色素沉着。这表明TT19基因是花色苷液泡摄取所必需的，但它还具有与AN9不同的功能。突变体中原花青素前体的沉积模式与野生型不同。这些结果表明，TT19参与了拟南芥的原花青素途径以及花色苷途径。由于之前认为GST不太可能参与原花青素途径，因此还在原花青素前体推定转运体的背景下讨论了TT19在原花青素途径中的功能。
