Tanaka Yoshiyuki, Nakashima Fumihiro, Kirii Erasmus, Goto Tanjuro, Yoshida Yuichi, Yasuba Ken-Ichiro
Graduate School of Environmental and Life Science, Okayama University, Okayama, 700-8530, Japan.
Plant Cell Rep. 2017 Feb;36(2):267-279. doi: 10.1007/s00299-016-2078-8. Epub 2016 Nov 21.
This research reveals that the up-regulated expression of multiple capsaicinoid biosynthetic genes in pericarp tissue leads to the elevation of total capsaicinoid content in chili pepper fruit. Capsaicinoids are health-functional compounds that are produced uniquely in chili pepper fruits. A high capsaicinoid level is one of the major parameters determining the commercial quality and health-promoting properties of chili peppers. To investigate the mechanisms responsible for its high contents, we compared an extremely pungent cultivar 'Trinidad Moruga Scorpion Yellow' (MY) with other cultivars of different pungency levels (Fushimi-amanaga, Takanotsume, Red Habanero). Capsaicinoid concentrations were markedly higher in MY fruit (23.9 mg/g DW) than in other pungent cultivars including 'Red Habanero' (HB) fruit (14.3 mg/g DW). Comparative analysis of MY and HB reveals that both cultivars accumulated similar capsaicinoid concentrations in the placental septum, with that in the HB pericarp (1.8 mg/g DW) being markedly lower than that in the placental septum (69.1 mg/g DW). The capsaicinoid concentration in HB fruit is dependent on the placental septum, as reported in other accessions. Therefore, even though placental septum tissue contains high capsaicinoid concentrations, those in the pericarp and seeds attenuated its total content. In contrast, the MY pericarp exhibited a markedly higher concentration (23.2 mg/g DW). A qRT-PCR analysis revealed that multiple capsaicinoid biosynthetic pathway genes (Pun1, pAMT, KAS, and BCAT) were strongly up-regulated in placental septum of pungent cultivars. The genes were expressed exclusively in the MY pericarp, but were barely detected in the pericarps of other pungent cultivars. Collectively, the present study indicates that the up-regulated expression of these genes not only in placental septum but also in pericarp plays an important role in driving capsaicinoid accumulation in the whole fruit.
本研究表明，辣椒果皮组织中多种辣椒素生物合成基因的表达上调导致辣椒果实中总辣椒素含量升高。辣椒素是辣椒果实中特有的具有健康功能的化合物。高辣椒素含量是决定辣椒商业品质和促进健康特性的主要参数之一。为了研究其高含量的形成机制，我们将极辣品种“特立尼达莫鲁加蝎子黄”（MY）与其他不同辣度的品种（福岛甘长、鹰爪、红哈瓦那）进行了比较。MY果实中的辣椒素浓度（23.9毫克/克干重）明显高于包括“红哈瓦那”（HB）果实（14.3毫克/克干重）在内的其他辣度品种。对MY和HB的比较分析表明，两个品种在胎座隔膜中积累的辣椒素浓度相似，而HB果皮中的辣椒素浓度（1.8毫克/克干重）明显低于胎座隔膜中的浓度（69.1毫克/克干重）。正如在其他材料中报道的那样，HB果实中的辣椒素浓度取决于胎座隔膜。因此，尽管胎座隔膜组织中辣椒素浓度很高，但果皮和种子中的辣椒素浓度降低了其总含量。相比之下，MY果皮表现出明显更高的浓度（23.2毫克/克干重）。定量逆转录聚合酶链反应（qRT-PCR）分析表明，多个辣椒素生物合成途径基因（Pun1、pAMT、KAS和BCAT）在辣度品种的胎座隔膜中强烈上调表达。这些基因仅在MY果皮中表达，但在其他辣度品种的果皮中几乎检测不到。总的来说，本研究表明，这些基因不仅在胎座隔膜中而且在果皮中的上调表达在驱动整个果实中辣椒素积累方面发挥着重要作用。
