Tomato plants (Solanum lycopersicum) contain steroidal glycoalkaloid α-tomatine, which functions as a chemical barrier to pathogens and predators. α-Tomatine accumulates in all tissues and at particularly high levels in leaves and immature green fruits. The compound is toxic and causes a bitter taste, but its presence decreases through metabolic conversion to nontoxic esculeoside A during fruit ripening. This study identifies the gene encoding a 23-hydroxylase of α-tomatine, which is a key to this process. Some 2-oxoglutarate-dependent dioxygenases were selected as candidates for the metabolic enzyme, and Solyc02g062460, designated Sl23DOX, was found to encode α-tomatine 23-hydroxylase. Biochemical analysis of the recombinant Sl23DOX protein demonstrated that it catalyzes the 23-hydroxylation of α-tomatine and the product spontaneously isomerizes to neorickiioside B, which is an intermediate in α-tomatine metabolism that appears during ripening. Leaves of transgenic tomato plants overexpressing Sl23DOX accumulated not only neorickiioside B but also another intermediate, lycoperoside C (23-O-acetylated neorickiioside B). Furthermore, the ripe fruits of Sl23DOX-silenced transgenic tomato plants contained lower levels of esculeoside A but substantially accumulated α-tomatine. Thus, Sl23DOX functions as α-tomatine 23-hydroxylase during the metabolic processing of toxic α-tomatine in tomato fruit ripening and is a key enzyme in the domestication of cultivated tomatoes.

中文翻译：

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苦糖生物碱解毒过程中α-托马汀23-羟化酶的鉴定。

番茄植物（茄属植物）含有类固醇生物碱α-番茄碱，对病原体和捕食者具有化学屏障作用。α-托马汀累积在所有组织中，并且在叶子和未成熟的绿色果实中含量特别高。该化合物有毒并引起苦味，但在果实成熟过程中，通过代谢转化为无毒七叶皂苷A可以减少化合物的存在。这项研究确定了编码α-番茄碱的23-羟化酶的基因，这是该过程的关键。选择一些2-氧戊二酸依赖性双加氧酶作为代谢酶的候选物，发现Slyc02g062460（命名为Sl23DOX）编码α-番茄碱23-羟化酶。重组Sl23DOX蛋白的生化分析表明，它催化α-番茄碱的23-羟基化作用，并且该产物自发异构化为新rickiioside B，后者是α-番茄碱代谢中的一个中间体，在成熟过程中会出现。过表达Sl23DOX的转基因番茄植株的叶子不仅积聚了新书草苷B，而且还积聚了另一种中间体番茄红素C（23-O-乙酰化的新书草苷B）。此外，Sl23DOX沉默的转基因番茄植株的成熟果实所含的七叶皂苷A含量较低，但α-番茄碱却大量积累。因此，Sl23DOX在番茄果实成熟过程中的有毒α-番茄碱的代谢过程中充当α-番茄碱23-羟化酶，并且是栽培番茄驯化中的关键酶。它是成熟过程中出现的α-番茄碱代谢的中间产物。过表达Sl23DOX的转基因番茄植株的叶子不仅积聚了新书草苷B，而且还积聚了另一种中间体番茄红素C（23-O-乙酰化的新书草苷B）。此外，Sl23DOX沉默的转基因番茄植株的成熟果实所含的七叶皂苷A含量较低，但α-番茄碱却大量积累。因此，Sl23DOX在番茄果实成熟过程中的有毒α-番茄碱的代谢过程中充当α-番茄碱23-羟化酶，并且是栽培番茄驯化中的关键酶。它是成熟过程中出现的α-番茄碱代谢的中间产物。过表达Sl23DOX的转基因番茄植株的叶子不仅积聚了新书草苷B，而且还积聚了另一种中间体番茄红素C（23-O-乙酰化的新书草苷B）。此外，Sl23DOX沉默的转基因番茄植株的成熟果实所含的七叶皂苷A含量较低，但α-番茄碱却大量积累。因此，Sl23DOX在番茄果实成熟过程中的有毒α-番茄碱的代谢过程中充当α-番茄碱23-羟化酶，并且是栽培番茄驯化中的关键酶。由Sl23DOX沉默的转基因番茄植株的成熟果实中的七叶皂苷A含量较低，但基本上富含α-番茄碱。因此，Sl23DOX在番茄果实成熟过程中的有毒α-番茄碱的代谢过程中充当α-番茄碱23-羟化酶，并且是栽培番茄驯化中的关键酶。由Sl23DOX沉默的转基因番茄植株的成熟果实中的七叶皂苷A含量较低，但基本上富含α-番茄碱。因此，Sl23DOX在番茄果实成熟过程中的有毒α-番茄碱的代谢过程中充当α-番茄碱23-羟化酶，并且是栽培番茄驯化中的关键酶。