Extrafloral nectaries are a defence trait that plays important roles in plant–animal interactions. Gossypium species are characterized by cellular grooves in leaf midribs that secret large amounts of nectar. Here, with a panel of 215 G. arboreum accessions, we compared extrafloral nectaries to nectariless accessions to identify a region of Chr12 that showed strong differentiation and overlapped with signals from GWAS of nectaries. Fine mapping of an F₂ population identified GaNEC1, encoding a PB1 domain‐containing protein, as a positive regulator of nectary formation. An InDel, encoding a five amino acid deletion, together with a nonsynonymous substitution, was predicted to cause 3D structural changes in GaNEC1 protein that could confer the nectariless phenotype. mRNA‐Seq analysis showed that JA‐related genes are up‐regulated and cell wall‐related genes are down‐regulated in the nectary. Silencing of GaNEC1 led to a smaller size of foliar nectary phenotype. Metabolomics analysis identified more than 400 metabolites in nectar, including expected saccharides and amino acids. The identification of GaNEC1 helps establish the network regulating nectary formation and nectar secretion, and has implications for understanding the production of secondary metabolites in nectar. Our results will deepen our understanding of plant–mutualism co‐evolution and interactions, and will enable utilization of a plant defence trait in cotton breeding efforts.

中文翻译：

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棉花花外蜜腺的遗传与进化分析

花外蜜腺是一种防御性状，在动植物相互作用中发挥着重要作用。棉属植物的特征是叶中脉上有细胞凹槽，可分泌大量花蜜。在这里，我们利用一组 215 个G. arboreum种质，将花外蜜腺与无蜜腺种质进行比较，以确定 Chr12 的一个区域，该区域表现出强烈的分化，并与蜜腺 GWAS 的信号重叠。_{F 2}群体的精细图谱鉴定出GaNEC1（编码含有 PB1 结构域的蛋白质）作为蜜腺形成的正调节因子。编码五个氨基酸缺失的 InDel 与非同义取代一起，预计会引起GaNEC1蛋白的 3D 结构变化，从而赋予无蜜腺表型。mRNA-Seq 分析表明，蜜腺中 JA 相关基因上调，细胞壁相关基因下调。GaNEC1的沉默导致叶蜜腺表型尺寸更小。代谢组学分析鉴定出花蜜中 400 多种代谢物，包括预期的糖类和氨基酸。GaNEC1的鉴定有助于建立调节蜜腺形成和花蜜分泌的网络，并对了解花蜜中次生代谢物的产生具有重要意义。我们的结果将加深我们对植物互利共进化和相互作用的理解，并将使植物防御性状在棉花育种工作中的利用成为可能。