Convergent evolution of a blood-red nectar pigment in vertebrate-pollinated flowers

第一作者：Rahul Roy

第一单位：明尼苏达大学

第一通讯：Clay J. Carter

 Abstarct 

背景回顾：Nearly 90% of flowering plants depend on animals for reproduction. One of the main rewards plants offer to pollinators for visitation is nectar. Nesocodon mauritianus (Campanulaceae) produces a blood-red nectar that has been proposed to serve as a visual attractant for pollinator visitation. 

大约90%的有花植物依赖于动物进行生殖。花蜜是植物用来吸引授粉者的主要手段之一。桔梗科的毛里求斯岛风铃会产生血色的花蜜，被认为是其吸引授粉者的视觉引诱剂。

主要发现：Here, we show that the nectar’s red color is derived from a previously undescribed alkaloid termed nesocodin. 

本文中，作者发现毛里求斯岛风铃花蜜的红色来源于一种先前未曾报道过的生物碱，作者将其命名为nesocodin（岛风铃素）。

结果1-岛风铃花蜜变化：The first nectar produced is acidic and pale yellow in color, but slowly becomes alkaline before taking on its characteristic red color. 

岛风铃的花蜜在刚开始产生时是酸性的，并且表现为淡黄色，而后在呈现其特有的红色之前，逐渐变为碱性。

结果2-血色色素形成的3个关键酶：Three enzymes secreted into the nectar are either necessary or sufficient for pigment production, including a carbonic anhydrase that increases nectar pH, an aryl-alcohol oxidase that produces a pigment precursor, and a ferritin-like catalase that protects the pigment from degradation by hydrogen peroxide. Our findings demonstrate how these three enzymatic activities allow for the condensation of sinapaldehyde and proline to form a pigment with a stable imine bond. 

岛风铃素的产生需要三种被分泌到岛风铃花蜜中的酶，一个是能够增加花蜜pH的碳酸酐酶，一个是能够形成岛风铃素前体的芳基醇氧化酶，最后一个是保护岛风铃素不被过氧化氢降解的类铁蛋白过氧化氢酶。作者发现这三个酶使得芥子醛和脯氨酸缩合，形成了具有稳定亚胺键的色素。

结果3-岛风铃素对传粉者的吸引：We subsequently verified that synthetic nesocodin is indeed attractive to Phelsuma geckos, the most likely pollinators of Nesocodon. 

作者随后证实了人工合成的岛风铃素的确对于岛风铃最有可能的授粉者，即日行壁虎具有吸引力。

结果4-趋同演化：We also identify nesocodin in the red nectar of the distantly related and hummingbird-visited Jaltomata herrerae and provide molecular evidence for convergent evolution of this trait. 

另外，作者还从远缘的茄科植物蜜钟茄（Jaltomata herrerae）红色花蜜中鉴定到了岛风铃素，进一步的证据显示这是趋同演化的结果。

结论：This work cumulatively identifies a convergently evolved trait in two vertebrate-pollinated species, suggesting that the red pigment is selectively favored and that only a limited number of compounds are likely to underlie this type of adaptation.

本文的研究在两种由不同脊椎动物传粉的远缘植物物种中，鉴定到了一种趋同演化的性状，表明红色色素是受选择青睐的，并且这种适应性演化的背后只需以少数几种化合物为基础。

** Clay J. Carter **

doi: https://doi.org/10.1073/pnas.2114420119

Journal: PNAS

Published date: February 01, 2022