Table_1_Genetic and physiological requirements for high-level sesquiterpene-production in tomato glandular trichomes.docx

Type-VI glandular trichomes of wild tomato Solanum habrochaites PI127826 produce high levels of the sesquiterpene 7-epizingiberene and its derivatives, making the plant repellent and toxic to several pest insects and pathogens. How wild tomato trichomes achieve such high terpene production is still largely unknown. Here we show that a cross (F1) with a cultivated tomato produced only minute levels of 7-epizingiberene. In the F2-progeny, selected for the presence of the 7-epizingiberene biosynthesis genes, only three percent produced comparable amounts the wild parent, indicating this trait is recessive and multigenic. Moreover, trichome density alone did not explain the total levels of terpene levels found on the leaves. We selected F2 plants with the “high-production active-trichome phenotype” of PI127826, having trichomes producing about 150 times higher levels of terpenes than F2 individuals that displayed a “low-production lazy-trichome phenotype”. Terpene quantities in trichomes of these F2 plants correlated with the volume of the storage cavity and shape of the gland. We found that trichome morphology is not a predetermined characteristic, but cavity volume rather depended on gland-cell metabolic activity. Inhibitor assays showed that the plastidial-precursor pathway (MEP) is fundamental for high-level production of both cytosolic as well as plastid-derived terpenes in tomato trichomes. Additionally, gene expression profiles of isolated secretory cells showed that key enzymes in the MEP pathway were higher expressed in active trichomes. We conclude that the MEP pathway is the primary precursor-supply route in wild tomato type-VI trichomes and that the high-production phenotype of the wild tomato trichome is indeed a multigenic trait.

野生番茄Solanum habrochaites PI127826的VI型腺毛（glandular trichome）能够合成高水平的倍半萜（sesquiterpene）7-表姜烯（7-epizingiberene）及其衍生物，使该植株对多种害虫与病原菌兼具驱避性与毒性。目前学界对野生番茄腺毛实现如此高萜类产量的机制仍知之甚少。本研究显示，与栽培番茄杂交获得的F1代仅能合成极微量的7-表姜烯。在筛选携带7-表姜烯生物合成基因的F2后代中，仅3%的个体能达到野生亲本的产量水平，表明该性状为隐性且受多基因调控。此外，仅腺毛密度无法解释叶片中检测到的总萜类含量。我们筛选出具有PI127826"高产活跃腺毛表型"的F2植株，其腺毛的萜类产量约为呈现"低产惰性腺毛表型"的F2个体的150倍。这些F2植株腺毛中的萜类含量与储藏腔体积及腺体形态显著相关。研究发现，腺毛形态并非固有特征，而储藏腔体积主要取决于腺细胞的代谢活性。抑制剂实验表明，质体前体途径（MEP途径）是番茄腺毛合成胞质及质体来源萜类的核心基础。此外，分离得到的分泌细胞的基因表达谱显示，MEP途径中的关键酶在活跃腺毛中表达量更高。综上，野生番茄VI型腺毛的主要前体供给通路为MEP途径，且野生番茄腺毛的高产表型确实为多基因调控性状。