Department of Biology, Texas A&M University, College Station, Texas 77843, USA.
Department of Chemistry, Texas A&M University, College Station, Texas 77843, USA.
Plant Physiol. 2023 Feb 12;191(2):1199-1213. doi: 10.1093/plphys/kiac487.
Acylsugars, specialized metabolites with defense activities, are secreted by trichomes of many solanaceous plants. Several acylsugar metabolic genes (AMGs) remain unknown. We previously reported multiple candidate AMGs. Here, using multiple approaches, we characterized additional AMGs. First, we identified differentially expressed genes between high- and low-acylsugar-producing F2 plants derived from a cross between cultivated tomato (Solanum lycopersicum) and a wild relative (Solanum pennellii), which produce acylsugars that are ∼1% and ∼20% of leaf dry weight, respectively. Expression levels of many known and candidate AMGs positively correlated with acylsugar amounts in F2 individuals. Next, we identified lycopersicum-pennellii putative orthologs with higher nonsynonymous to synonymous substitutions. These analyses identified four candidate genes, three of which showed enriched expression in stem trichomes compared to underlying tissues (shaved stems). Virus-induced gene silencing confirmed two candidates, Sopen05g009610 [beta-ketoacyl-(acyl-carrier-protein) reductase; fatty acid synthase component] and Sopen07g006810 (Rubisco small subunit), as AMGs. Phylogenetic analysis indicated that Sopen05g009610 is distinct from specialized metabolic cytosolic reductases but closely related to two capsaicinoid biosynthetic reductases, suggesting evolutionary relationship between acylsugar and capsaicinoid biosynthesis. Analysis of publicly available datasets revealed enriched expression of Sopen05g009610 orthologs in trichomes of several acylsugar-producing species. Similarly, orthologs of Sopen07g006810 were identified as solanaceous trichome-enriched members, which form a phylogenetic clade distinct from those of mesophyll-expressed "regular" Rubisco small subunits. Furthermore, δ13C analyses indicated recycling of metabolic CO2 into acylsugars by Sopen07g006810 and showed how trichomes support high levels of specialized metabolite production. These findings have implications for genetic manipulation of trichome-specialized metabolism in solanaceous crops.
酰基糖是具有防御功能的特殊代谢物，由许多茄科植物的毛状体分泌。一些酰基糖代谢基因（AMGs）仍然未知。我们之前报道了多个候选 AMGs。在这里，我们使用多种方法对其他 AMGs 进行了表征。首先，我们鉴定了来自栽培番茄（Solanum lycopersicum）和野生亲缘种（Solanum pennellii）杂交产生的高和低酰基糖产生的 F2 植物之间差异表达的基因。这些植物的酰基糖含量分别约占叶片干重的 1%和 20%。许多已知和候选 AMGs 的表达水平与 F2 个体中酰基糖的含量呈正相关。接下来，我们鉴定了 Lycopersicum-pennellii 具有更高非同义与同义替换的假定直系同源物。这些分析鉴定了四个候选基因，其中三个在茎毛状体中的表达比在其下组织（刮茎）中更丰富。病毒诱导的基因沉默证实了两个候选基因 Sopen05g009610（β-酮酰基-（酰基载体蛋白）还原酶；脂肪酸合酶组件）和 Sopen07g006810（Rubisco 小亚基）是 AMGs。系统发育分析表明，Sopen05g009610 与专门的代谢细胞质还原酶不同，但与两种辣椒素生物合成还原酶密切相关，表明酰基糖和辣椒素生物合成之间存在进化关系。对公开可用数据集的分析表明，几种酰基糖产生物种的毛状体中 Sopen05g009610 同源物的表达丰富。类似地，Sopen07g006810 的同源物被鉴定为茄科毛状体丰富的成员，它们形成了一个与叶片表达的“常规”Rubisco 小亚基不同的系统发育分支。此外，δ13C 分析表明 Sopen07g006810 将代谢 CO2 再循环到酰基糖中，并说明了毛状体如何支持高水平的特殊代谢产物产生。这些发现对茄科作物毛状体特殊代谢的遗传操作具有重要意义。
