Kato Keita, Shoji Tsubasa, Hashimoto Takashi
Graduate School of Biological Sciences, Nara Institute of Science and Technology, Ikoma, Nara 630-0192, Japan.
Graduate School of Biological Sciences, Nara Institute of Science and Technology, Ikoma, Nara 630-0192, Japan
Plant Physiol. 2014 Dec;166(4):2195-204. doi: 10.1104/pp.114.251645. Epub 2014 Oct 24.
The down-regulation of a tobacco (Nicotiana tabacum) plasma membrane-localized nicotine uptake permease, NUP1, was previously reported to reduce total alkaloid levels in tobacco plants. However, it was unclear how this nicotine transporter affected the biosynthesis of the alkaloid nicotine. When NUP1 expression was suppressed in cultured tobacco cells treated with jasmonate, which induces nicotine biosynthesis, the NICOTINE2-locus transcription factor gene ETHYLENE RESPONSE FACTOR189 (ERF189) and its target structural genes, which function in nicotine biosynthesis and transport, were strongly suppressed, resulting in decreased total alkaloid levels. Conversely, NUP1 overexpression had the opposite effect. In these experiments, the expression levels of the MYC2 transcription factor gene and its jasmonate-inducible target gene were not altered. Inhibiting tobacco alkaloid biosynthesis by suppressing the expression of genes encoding enzymes in the nicotine pathway did not affect the expression of ERF189 and other nicotine pathway genes, indicating that ERF189 is not regulated by cellular alkaloid levels. Suppressing the expression of jasmonate signaling components in cultured tobacco cells showed that NUP1 acts downstream of the CORONATINE INSENSITIVE1 receptor and MYC2, but upstream of ERF189. These results suggest that although jasmonate-activated expression of MYC2 induces the expression of both NUP1 and ERF189, expression of ERF189 may actually be mediated by NUP1. Furthermore, NUP1 overexpression in tobacco plants inhibited the long-range transport of nicotine from the roots to the aerial parts. Thus, NUP1 not only mediates the uptake of tobacco alkaloids into root cells, but also positively controls the expression of ERF189, a key gene in the biosynthesis of these alkaloids.
先前有报道称，烟草（Nicotiana tabacum）质膜定位的尼古丁摄取通透酶NUP1的下调会降低烟草植株中的总生物碱水平。然而，尚不清楚这种尼古丁转运蛋白如何影响生物碱尼古丁的生物合成。在用茉莉酸处理的培养烟草细胞中，茉莉酸可诱导尼古丁生物合成，当NUP1表达受到抑制时，在尼古丁生物合成和转运中起作用的NICOTINE2位点转录因子基因乙烯反应因子189（ERF189）及其靶结构基因受到强烈抑制，导致总生物碱水平降低。相反，NUP1过表达则产生相反的效果。在这些实验中，MYC2转录因子基因及其茉莉酸诱导型靶基因的表达水平没有改变。通过抑制尼古丁途径中编码酶的基因表达来抑制烟草生物碱生物合成，并不影响ERF189和其他尼古丁途径基因的表达，这表明ERF189不受细胞生物碱水平的调控。在培养的烟草细胞中抑制茉莉酸信号成分的表达表明，NUP1作用于不敏感冠菌素1受体和MYC2的下游，但在ERF189的上游。这些结果表明，尽管茉莉酸激活的MYC2表达诱导了NUP1和ERF189的表达，但ERF189的表达实际上可能由NUP1介导。此外，烟草植株中NUP1的过表达抑制了尼古丁从根部到地上部分的长距离运输。因此，NUP1不仅介导烟草生物碱进入根细胞的摄取，还正向调控这些生物碱生物合成中的关键基因ERF189的表达。
