As one of the most destructive pests, aphids cause significant damage on various agricultural and horticultural crops. Recently, melatonin has been shown to enhance plant resistance to aphids; however, the underlying mechanisms remain unclear. In this study, our results showed that melatonin, MeJA, and H₂S enhanced aphid resistance of watermelon in a dose-dependent manner, accompanied by increases in the defense-related enzyme activities and lignin accumulation. On the plants pretreated with 100 μM melatonin, 100 μM MeJA, and 50 μM NaHS, the numbers of aphids were 86.0%, 59.6%, and 47.9% lower than that on control plants, respectively, after aphid infestation for 7 days. Melatonin application induced MeJA and H₂S accumulation in response to aphid infestation, while inhibition of MeJA and H₂S accumulation attenuated or abolished melatonin-induced defense response and aphid resistance, suggestive of the involvement of MeJA and H₂S in melatonin-induced aphid resistance. MeJA also increased H₂S accumulation, but inhibition of MeJA biosynthesis prevented melatonin-enhanced H₂S accumulation, suggesting that MeJA mediates melatonin-induced H₂S accumulation. Furthermore, inhibition of H₂S production attenuated MeJA-induced defense response and aphid resistance. Taken together, the current study reveals a novel mechanism in which MeJA-dependent H₂S signaling is involved in melatonin-induced defense response and subsequent aphid resistance. The increasing concern to minimize the use of pesticides and to switch onto sustainable and natural control strategies indicates the great exploitation of such a mechanism in combating aphids.

中文翻译：

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茉莉酸甲酯依赖性硫化氢介导褪黑素诱导的西瓜蚜虫抗性

蚜虫作为最具破坏性的害虫之一，对各种农业和园艺作物造成重大损害。最近，褪黑激素已被证明可以增强植物对蚜虫的抵抗力；然而，其根本机制仍不清楚。在本研究中，我们的结果表明，褪黑素、MeJA 和 H ₂ S 以剂量依赖性方式增强西瓜的蚜虫抗性，同时伴随着防御相关酶活性和木质素积累的增加。在用100μM褪黑素、100μM MeJA和50μM NaHS预处理的植物上，蚜虫侵染7天后，蚜虫数量分别比对照植物减少86.0%、59.6%和47.9%。褪黑激素应用诱导 MeJA 和 H ₂S积累响应蚜虫侵染，而抑制MeJA和H ₂ S积累则减弱或消除褪黑素诱导的防御反应和蚜虫抗性，表明MeJA和H ₂ S参与褪黑素诱导的蚜虫抗性。MeJA 还增加 H ₂ S 积累，但抑制 MeJA 生物合成可阻止褪黑激素增强的 H ₂ S 积累，表明 MeJA 介导褪黑激素诱导的 H ₂ S 积累。此外，H ₂ S产生的抑制减弱了MeJA诱导的防御反应和蚜虫抗性。总而言之，当前的研究揭示了一种新的机制，其中依赖 MeJA 的 H ₂S信号传导参与褪黑激素诱导的防御反应和随后的蚜虫抗性。人们越来越关注尽量减少农药的使用并转向可持续和自然的控制策略，这表明这种机制在防治蚜虫方面得到了广泛的利用。