Katzer Amanda M, Wessinger Carolyn A, Anaya Brooklyn M, Hileman Lena C
Department of Ecology and Evolutionary Biology, University of Kansas, Lawrence, 66045, Kansas, USA.
Am J Bot. 2025 Jun;112(6):e70058. doi: 10.1002/ajb2.70058. Epub 2025 Jun 16.
Plants secrete carbohydrate-rich nectar from specialized floral nectary glands to attract pollinators. Arabidopsis and Petunia (rosid and asterid core eudicots, respectively) share genetic control of nectary development requiring activation of CRABS CLAW by euAGAMOUS and PLENA. This module is conserved despite striking differences in nectary morphology between the two species. We tested whether the euAGAMOUS/PLENA-CRABS CLAW module likely extends to an asterid species with novel nectary morphology, Penstemon barbatus.
To test conservation of the euAGAMOUS/PLENA-CRABS CLAW module and nectar sugar metabolism in P. barbatus, we carried out comparative transcriptomics, leveraging Penstemon's unique nectary morphology. Specifically, lateral and ventral stamen filaments develop with and without nectaries at their base, respectively, allowing straightforward differential expression analyses to uncover nectary-specific gene expression.
Many genes were differentially expressed between nectary and non-nectary tissues, and pre- and post-nectar-removal. Differentially expressed genes pointed to key phloem, abaxial specification, and epidermal cell shape functions during nectary development. Differentially expressed genes pointed to regulation of sugar processing and secretion after nectary maturation.
Our results suggest that P. barbatus nectaries develop independently of the canonical core-eudicot CRABS CLAW genetic module, despite being positioned within reproductive floral organ whorls, and that P. barbatus nectar production follows conserved sugar metabolic pathways.
植物从专门的花蜜腺分泌富含碳水化合物的花蜜以吸引传粉者。拟南芥和矮牵牛（分别为蔷薇类和菊类核心真双子叶植物）在花蜜发育的遗传控制方面具有共性，即需要euAGAMOUS和PLENA激活CRABS CLAW。尽管这两个物种的花蜜形态存在显著差异，但该模块是保守的。我们测试了euAGAMOUS/PLENA - CRABS CLAW模块是否可能扩展到具有新颖花蜜形态的菊类物种髯毛钓钟柳。
为了测试髯毛钓钟柳中euAGAMOUS/PLENA - CRABS CLAW模块和花蜜糖代谢的保守性，我们利用钓钟柳独特的花蜜形态进行了比较转录组学研究。具体而言，侧生和腹生雄蕊花丝分别在基部有和没有花蜜的情况下发育，这使得可以直接进行差异表达分析以揭示花蜜特异性基因表达。
花蜜组织与非花蜜组织之间以及去除花蜜前后有许多基因差异表达。差异表达基因表明在花蜜发育过程中关键的韧皮部、远轴面特化和表皮细胞形状功能。差异表达基因表明在花蜜成熟后对糖加工和分泌的调节。
我们的结果表明，尽管髯毛钓钟柳的花蜜位于生殖花器官轮中，但其花蜜发育独立于典型的核心真双子叶植物CRABS CLAW遗传模块，并且髯毛钓钟柳的花蜜产生遵循保守的糖代谢途径。
