背景回顾：Abscisic acid (ABA) is an important carotenoid-derived phytohormone that plays essential roles in plant response to biotic and abiotic stresses as well as in various physiological and developmental processes. 

原有途径：In Arabidopsis, ABA biosynthesis starts with the epoxidation of zeaxanthin by the ABA DEFICIENT 1 (ABA1) enzyme, leading to epoxycarotenoids, e.g., violaxanthin. The oxidative cleavage of 9-cis-epoxycarotenoids, a key regulatory step catalyzed by 9-CIS-EPOXYCAROTENOID DIOXYGENASE (NCED), forms xanthoxin that is converted in further reactions mediated by ABA DEFICIENT 2 (ABA2), ABA DEFICIENT 3 (ABA3), and ABSCISIC ALDEHYDE OXIDASE 3 (AAO3) into ABA.

主要发现：By combining genetic and biochemical approaches, we unravel here an ABA1-independent ABA biosynthetic pathway starting upstream of zeaxanthin. 

结果1-类胡萝卜素衍生物：We identified the carotenoid cleavage products, i.e., apocarotenoids, β-apo-11-carotenal, 9-cis-β-apo-11-carotenal, 3-OH-β-apo-11-carotenal, and 9-cis-3-OH-β-apo-11-carotenal as intermediates of this ABA1-independent ABA biosynthetic pathway. 

结果2-ABA合成新途径：Using labeled compounds, we showed that β-apo-11-carotenal, 9-cis-β-apo-11-carotenal, and 3-OH-β-apo-11-carotenal are successively converted into 9-cis-3-OH-β-apo-11-carotenal, xanthoxin, and finally into ABA in both Arabidopsis and rice. 

结果3-β-apo-11-carotenoids功能：When applied to Arabidopsis, these β-apo-11-carotenoids exert ABA biological functions, such as maintaining seed dormancy and inducing the expression of ABA-responsive genes. 

结果4-转录组分析：Indeed, the transcriptomic analysis revealed a high overlap of differentially expressed genes regulated by β-apo-11-carotenoids and ABA, but also suggested that these compounds exert ABA-independent regulatory activities. 

结论：Taken together, our study identifies a biological function for the common plant metabolites β-apo-11-carotenoids, extends our knowledge about ABA biosynthesis and provides new insights into plant apocarotenoid metabolic networks.

 摘 要 

脱落酸ABA是一种类胡萝卜素衍生物，作为重要的植物激素在植物响应生物和非生物胁迫以及在植物不同生理和发育进程中发挥关键作用。在拟南芥中，ABA的生物合成起始于ABA1酶介导的玉米黄质环氧化作用，形成环氧类胡萝卜素，即紫黄质。9-cis-环氧类胡萝卜素会被NCED氧化裂解，形成黄氧素，然后黄氧素会被ABA2、ABA3和AAO3进一步催化形成ABA。通过结合遗传和生化试验，作者发现了一个不依赖于ABA1的ABA生物合成通路，该通路起始于玉米黄质的上游。作者发现胡萝卜素裂解产物脱辅基类胡萝卜素（apocarotenoids）、β-apo-11-carotenal、9-cis-β-apo-11-carotenal、3-OH-β-apo-11-carotenal和9-cis-3-OH-β-apo-11-carotenal是不依赖于ABA1的ABA生物合成通路的中间产物。利用标记的化合物，作者发现在拟南芥和水稻中，β-apo-11-carotenal、9-cis-β-apo-11-carotenal和3-OH-β-apo-11-carotenal会被依次转化为9-cis-3-OH-β-apo-11-carotenal、黄氧素以及最后的ABA。作者用β-apo-11-carotenoids处理拟南芥，发现其具有ABA的生物功能，比如维持种子休眠和诱导ABA响应基因的表达。确实，转录组分析显示受β-apo-11-carotenoid和受ABA诱导差异表达的基因之间存在很大程度的重叠，但同时也说明了这些化合物还存在不依赖于ABA的调控活性。综上，本文的研究鉴定了常见植物代谢物β-apo-11-carotenoids的一个生物学功能，拓展了我们对于ABA生物合成的理解，同时也为植物脱辅基类胡萝卜素代谢网络提供了新的视野。