College of Resources and Environment, Fujian Agriculture and Forestry University, No. 15 Shangxiadian Road, Cangshan, Fuzhou 350002, China.
College of Environmental and Biological Engineering, Putian University, No. 1133 Xueyuan Middle Street, Chengxiang, Putian 351100, China.
Tree Physiol. 2024 Sep 3;44(9). doi: 10.1093/treephys/tpae099.
Both copper (Cu) excess and boron (B) deficiency are often observed in some citrus orchard soils. The molecular mechanisms by which B alleviates excessive Cu in citrus are poorly understood. Seedlings of sweet orange (Citrus sinensis (L.) Osbeck cv. Xuegan) were treated with 0.5 (Cu0.5) or 350 (Cu350 or Cu excess) μM CuCl2 and 2.5 (B2.5) or 25 (B25) μM HBO3 for 24 wk. Thereafter, this study examined the effects of Cu and B treatments on gene expression levels revealed by RNA-Seq, metabolite profiles revealed by a widely targeted metabolome, and related physiological parameters in leaves. Cu350 upregulated 564 genes and 170 metabolites, and downregulated 598 genes and 58 metabolites in leaves of 2.5 μM B-treated seedlings (LB2.5), but it only upregulated 281 genes and 100 metabolites, and downregulated 136 genes and 40 metabolites in leaves of 25 μM B-treated seedlings (LB25). Cu350 decreased the concentrations of sucrose and total soluble sugars and increased the concentrations of starch, glucose, fructose and total nonstructural carbohydrates in LB2.5, but it only increased the glucose concentration in LB25. Further analysis demonstrated that B addition reduced the oxidative damage and alterations in primary and secondary metabolisms caused by Cu350, and alleviated the impairment of Cu350 to photosynthesis and cell wall metabolism, thus improving leaf growth. LB2.5 exhibited some adaptive responses to Cu350 to meet the increasing need for the dissipation of excessive excitation energy (EEE) and the detoxification of reactive oxygen species (reactive aldehydes) and Cu. Cu350 increased photorespiration, xanthophyll cycle-dependent thermal dissipation, nonstructural carbohydrate accumulation, and secondary metabolite biosynthesis and abundances; and upregulated tryptophan metabolism and related metabolite abundances, some antioxidant-related gene expression, and some antioxidant abundances. Additionally, this study identified some metabolic pathways, metabolites and genes that might lead to Cu tolerance in leaves.
铜（Cu）过量和硼（B）缺乏通常在一些柑橘园土壤中观察到。B 缓解柑橘中过量 Cu 的分子机制知之甚少。用 0.5（Cu0.5）或 350（Cu350 或 Cu 过量）μM CuCl2 和 2.5（B2.5）或 25（B25）μM HBO3 处理甜橙（Citrus sinensis（L.）Osbeck cv. Xuegan）幼苗 24 周。此后，本研究通过 RNA-Seq 检测基因表达水平，通过广泛靶向代谢组学检测代谢物谱，以及叶片相关生理参数，研究了 Cu 和 B 处理对叶片的影响。Cu350 在 2.5μMB 处理的幼苗（LB2.5）叶片中上调了 564 个基因和 170 种代谢物，下调了 598 个基因和 58 种代谢物，但仅上调了 281 个基因和 100 种代谢物，下调了 136 个基因和 40 种代谢物在 25μMB 处理的幼苗（LB25）叶片中。Cu350 降低了蔗糖和总可溶性糖的浓度，增加了淀粉、葡萄糖、果糖和总非结构性碳水化合物的浓度在 LB2.5 中，但仅增加了 LB25 中的葡萄糖浓度。进一步分析表明，B 的添加减少了 Cu350 引起的氧化损伤和初级和次级代谢物的改变，并缓解了 Cu350 对光合作用和细胞壁代谢的损害，从而促进了叶片生长。LB2.5 对 Cu350 表现出一些适应性反应，以满足过量激发能（EEE）和活性氧（反应醛）和 Cu 解毒的增加需求。Cu350 增加了光呼吸、叶黄素循环依赖性热耗散、非结构性碳水化合物积累以及次生代谢物的生物合成和丰度；并上调了色氨酸代谢及相关代谢物丰度、一些抗氧化相关基因表达和一些抗氧化剂丰度。此外，本研究还鉴定了一些可能导致叶片 Cu 耐受的代谢途径、代谢物和基因。
