Heavy metal pollution not only decreases crop yield and quality, but also affects human health via the food chain. Ubiquitination-dependent protein degradation is involved in plant growth, development, and environmental interaction, but the functions of ubiquitin-ligase (E3) genes are largely unknown in tomato (Solanum lycopersicum L.). Here, we functionally characterized a RING E3 ligase gene, SlRING1, which positively regulates cadmium (Cd) tolerance in tomato plants. An in vitro ubiquitination experiment shows that SlRING1 has E3 ubiquitin ligase activity. The determination of the subcellular localization reveals that SlRING1 is localized at both the plasma membrane and the nucleus. Overexpression of SlRING1 in tomato increased the chlorophyll content, the net photosynthetic rate, and the maximal photochemical efficiency of photosystem II (Fv/Fm), but reduced the levels of reactive oxygen species and relative electrolyte leakage under Cd stress. Moreover, SlRING1 overexpression increased the transcript levels of CATALASE (CAT), DEHYDROASCORBATE REDUCTASE (DHAR), MONODEHYDROASCORBATE REDUCTASE (MDHAR), GLUTATHIONE (GSH1), and PHYTOCHELATIN SYNTHASE (PCS), which contribute to the antioxidant and detoxification system. Crucially, SlRING1 overexpression also reduced the concentrations of Cd in both shoots and roots. Thus, SlRING1-overexpression-induced enhanced tolerance to Cd is ascribed to reduced Cd accumulation and alleviated oxidative stress. Our findings suggest that SlRING1 is a positive regulator of Cd tolerance, which can be a potential breeding target for improving heavy metal tolerance in horticultural crops.

中文翻译：

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番茄 RING E3 泛素连接酶基因 SlRING1 的过表达通过减弱镉积累和氧化应激赋予镉耐受性

重金属污染不仅会降低作物产量和质量，还会通过食物链影响人类健康。泛素化依赖性蛋白质降解参与植物生长、发育和环境相互作用，但泛素连接酶 (E3) 基因在番茄 ( Solanum lycopersicum L.) 中的功能在很大程度上是未知的。在这里，我们对 RING E3 连接酶基因SlRING1 进行了功能表征，该基因正向调节番茄植物的镉 (Cd) 耐受性。体外泛素化实验表明，SlRING1 具有 E3 泛素连接酶活性。亚细胞定位的测定表明 SlRING1 定位于质膜和细胞核。SlRING1 的过度表达番茄中的叶绿素含量、净光合速率和光系统 II 的最大光化学效率 (Fv/Fm) 增加，但在镉胁迫下降低了活性氧水平和相对电解质泄漏。此外，SlRING1过表达增加了过氧化氢酶 (CAT)、脱氢抗坏血酸还原酶 (DHAR)、单脱氢抗坏血酸还原酶 (MDHAR)、谷胱甘肽 (GSH1)和植物螯合素合成酶 (PCS)的转录水平，这些都有助于抗氧化系统和脱氢酶。至关重要的是，SlRING1过表达也降低了芽和根中 Cd 的浓度。因此，SlRING1-过表达诱导对 Cd 的耐受性增强归因于减少的 Cd 积累和减轻的氧化应激。我们的研究结果表明，SlRING1是 Cd 耐受性的正调节因子，可以作为提高园艺作物重金属耐受性的潜在育种目标。