The tomato non-ripening (nor) mutant generates a truncated 186-amino-acid protein (NOR186) and has been demonstrated previously to be a gain-of-function mutant. Here, we provide more evidence to support this view and answer the open question of whether the NAC-NOR gene is important in fruit ripening. Overexpression of NAC-NOR in the nor mutant did not restore the full ripening phenotype. Further analysis showed that the truncated NOR186 protein is located in the nucleus and binds to but does not activate the promoters of 1-aminocyclopropane-1-carboxylic acid synthase2 (SlACS2), geranylgeranyl diphosphate synthase2 (SlGgpps2), and pectate lyase (SlPL), which are involved in ethylene biosynthesis, carotenoid accumulation, and fruit softening, respectively. The activation of the promoters by the wild-type NOR protein can be inhibited by the mutant NOR186 protein. On the other hand, ethylene synthesis, carotenoid accumulation, and fruit softening were significantly inhibited in CR-NOR (CRISPR/Cas9-edited NAC-NOR) fruit compared with the wild-type, but much less severely affected than in the nor mutant, while they were accelerated in OE-NOR (overexpressed NAC-NOR) fruit. These data further indicated that nor is a gain-of-function mutation and NAC-NOR plays a significant role in ripening of wild-type fruit.

中文翻译：

---

重新评估NOR突变以及NAC-NOR转录因子在番茄果实成熟中的作用。

番茄非成熟（nor）突变体产生186个氨基酸的截短蛋白（NOR186），以前已被证明是功能增强型突变体。在这里，我们提供了更多的证据来支持这种观点，并回答了NAC-NOR基因在果实成熟中是否重要的开放性问题。NAC - NOR在nor突变体中的过表达不能恢复完全成熟的表型。进一步的分析表明，截短的NOR186蛋白位于细胞核中，与1-氨基环丙烷-1-甲酸合酶2（SlACS2），香叶基香叶基二磷酸合酶2（SlGgpps2）的启动子结合但不激活）和果胶酸裂合酶（SlPL），分别参与乙烯的生物合成，类胡萝卜素的积累和果实的软化。突变型NOR186蛋白可以抑制野生型NOR蛋白对启动子的激活。另一方面，与野生型相比，CR-NOR（CRISPR / Cas9编辑的NAC-NOR）果实的乙烯合成，类胡萝卜素积累和果实软化受到显着抑制，但受影响程度不如nor突变体，而它们在OE-NOR（过表达的NAC-NOR）果实中得到加速。这些数据进一步表明，功能获得突变也不是，NAC-NOR在野生型果实的成熟中也起着重要作用。