Ascorbic acid (AsA) is a multifunctional phytonutrient that is essential for the human diet as well as plant development. While much is known about AsA biosynthesis in plants, how this process is regulated in tomato (Solanum lycopersicum) fruits remains unclear. Here, we found that auxin treatment inhibited AsA accumulation in the leaves and pericarps of tomato. The auxin response factor gene SlARF4 is induced by auxin to mediate auxin-induced inhibition of AsA accumulation. Specifically, SlARF4 transcriptionally inhibits the transcription factor gene SlMYB11, thereby modulating AsA accumulation by regulating the transcription of the AsA biosynthesis genes l-galactose-1-phosphate phosphatase, l-galactono-1,4-lactone dehydrogenase, and dehydroascorbate. By contrast, abscisic acid (ABA) treatment increased AsA accumulation in tomato under drought stress. ABA induced the expression of the mitogen-activated protein kinase gene SlMAPK8. We demonstrate that SlMAPK8 phosphorylates SlARF4 and inhibits its transcriptional activity, whereas SlMAPK8 phosphorylates SlMYB11 and activates its transcriptional activity. SlMAPK8 functions in ABA-induced AsA accumulation and drought stress tolerance. Moreover, ABA antagonizes the effects of auxin on AsA biosynthesis. Therefore, auxin- and ABA-induced regulation of AsA accumulation is mediated by the SlMAPK8-SlARF4-SlMYB11 module in tomato during fruit development and drought stress responses, shedding light on the roles of phytohormones in regulating AsA accumulation to mediate stress tolerance.

中文翻译：

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生长素和脱落酸通过番茄中的 SlMAPK8-SlARF4-SlMYB11 模块拮抗调节抗坏血酸的产生。

抗坏血酸 (AsA) 是一种多功能植物营养素，对于人类饮食和植物发育至关重要。虽然人们对植物中 AsA 的生物合成了解很多，但番茄 (Solanum lycopersicum) 果实中这一过程是如何调节的仍不清楚。在这里，我们发现生长素处理抑制了番茄叶片和果皮中 AsA 的积累。生长素反应因子基因 SlARF4 由生长素诱导，介导生长素诱导的 AsA 积累抑制。具体来说，SlARF4在转录上抑制转录因子基因SlMYB11，从而通过调节AsA生物合成基因l-半乳糖-1-磷酸磷酸酶、l-半乳糖-1,4-内酯脱氢酶和脱氢抗坏血酸的转录来调节AsA积累。相比之下，脱落酸 (ABA) 处理增加了干旱胁迫下番茄中 AsA 的积累。ABA 诱导丝裂原激活蛋白激酶基因 SlMAPK8 的表达。我们证明SlMAPK8磷酸化SlARF4并抑制其转录活性，而SlMAPK8磷酸化SlMYB11并激活其转录活性。SlMAPK8 在 ABA 诱导的 AsA 积累和干旱胁迫耐受中发挥作用。此外，ABA 拮抗生长素对 AsA 生物合成的影响。因此，在果实发育和干旱胁迫反应期间，生长素和ABA诱导的AsA积累调节是由番茄中的SlMAPK8-SlARF4-SlMYB11模块介导的，揭示了植物激素在调节AsA积累以介导胁迫耐受性中的作用。