Salicylic acid (SA) is a prominent defense hormone whose basal level, organ-specific accumulation, and physiological role vary widely among plant species. Of the two known pathways of plant SA biosynthesis, the phenylalanine ammonia lyase (PAL) pathway is more ancient and universal but its biosynthetic and physiological roles in diverse plant species remain unclear. Studies in which the PAL pathway is specifically or completely inhibited, as well as a direct comparison of diverse species and different organs within the same species, are needed. To this end, we analyzed the PAL pathway in rice (Oryza sativa) and Arabidopsis (Arabidopsis thaliana), two distantly related model plants whose basal SA levels and distributions differ tremendously at the organism and tissue levels. Based on our recent identification of the rice peroxisomal cinnamate:CoA ligases (CNLs), we identified two peroxisomal CNLs from Arabidopsis and showed CNL as the most functionally specific enzyme among the known enzymes of the PAL pathway. We then revealed the species- and organ-specific contribution of the PAL pathway to benzoic and salicylic acid biosynthesis and clarified its physiological importance in rice and Arabidopsis. Our findings highlight the necessity to consider species and organ types in future SA-related studies and may help to breed new disease-resistant crops.

中文翻译：

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过氧化物酶体肉桂酸：CoA 连接酶对苯甲酸和水杨酸生物合成的物种和器官特异性贡献


水杨酸 （SA） 是一种重要的防御激素，其基础水平、器官特异性积累和生理作用在植物物种之间差异很大。在植物 SA 生物合成的两种已知途径中，苯丙氨酸解氨酶 （PAL） 途径更古老和普遍，但其在不同植物物种中的生物合成和生理作用仍不清楚。需要对 PAL 通路进行特异性或完全抑制的研究，以及对不同物种和同一物种内的不同器官进行直接比较。为此，我们分析了水稻 （Oryza sativa） 和拟南芥 （Arabidopsis thaliana） 中的 PAL 通路，这两种关系相距甚远的模式植物，其基部 SA 水平和分布在生物体和组织水平上差异很大。基于我们最近对水稻过氧化物酶体肉桂酸：CoA 连接酶 （CNL） 的鉴定，我们从拟南芥中鉴定了两个过氧化物酶体 CNL，并显示 CNL 是 PAL 通路已知酶中功能特异性最强的酶。然后，我们揭示了 PAL 途径对苯甲酸和水杨酸生物合成的物种和器官特异性贡献，并阐明了其在水稻和拟南芥中的生理重要性。我们的研究结果强调了在未来 SA 相关研究中考虑物种和器官类型的必要性，并可能有助于培育新的抗病作物。