The morphology, molecular development and ecological function of pseudonectaries on Nigella damascena (Ranunculaceae) petals

First author: Hong Liao; Affiliations: CAS Institute of Botany (中科院植物所): Beijing, China

Corresponding author: Hongzhi Kong

Pseudonectaries (假蜜腺), or false nectaries, the glistening structures that resemble nectaries or nectar droplets but do not secrete nectar, show considerable diversity and play important roles in plant-animal interactions. The morphological nature, optical features, molecular underpinnings and ecological functions of pseudonectaries, however, remain largely unclear. Here, we show that pseudonectaries of Nigella damascena (Ranunculaceae) are tiny, regional protrusions covered by tightly arranged, non-secretory polygonal epidermal cells with flat, smooth and reflective surface, and are clearly visible even under ultraviolet light and bee vision. We also show that genes associated with cell division, chloroplast development and wax formation are preferably expressed in pseudonectaries. Specifically, NidaYABB5, an abaxial gene with ectopic expression in pseudonectaries, is indispensable for pseudonectary development: knockdown of it led to complete losses of pseudonectaries. Notably, when flowers without pseudonectaries were arrayed beside those with pseudonectaries, clear differences were observed in the visiting frequency, probing time and visiting behavior of pollinators (i.e., honey bees), suggesting that pseudonectaries serve as both visual attractants and nectar guides.

假蜜腺（pseudonectaries）是植物中一种外表上闪闪发光的结构，神似于植物的蜜腺或花蜜滴，但是并不分泌花蜜，在植物中具有非常高的多样性，并且在植物与动物的互作中扮演着非常重要的作用。然而，有关植物假蜜腺的形态学特性、光学特征、分子基础以及生态功能还存在较多的未知。本文中，作者发现毛茛科植物黑种草（Nigella damascena）的假蜜腺十分小，局部突起，并由紧密排列、不具分泌功能的多边形表皮细胞所覆盖，覆盖表面十分平坦、光滑并具有反射性，并且即使在紫外线下或是蜜蜂视野中也是清晰可见的。作者还发现与细胞分裂、叶绿体发育以及蜡质形成相关的基因在假蜜腺中存在优先表达。尤其是一个背轴基因NidaYABB5在假蜜腺中存在异位表达，而这对于假蜜腺的发育是不可或缺的，NidaYABB5基因的敲除突变体会完全丧失假蜜腺。有趣的是，将有无假蜜腺的花放在一起，会发现二者在传粉昆虫的到访频率、访花时间以及访花行为都存在明显的差异，说明了假蜜腺同时通过视觉引诱和花蜜引导发挥功能。

通讯：孔宏智（http://sourcedb.ib.cas.cn/cn/expert/201110/t20111006_3358925.html)

个人简介：1995年，西北大学，学士；2000年，中国科学院植物研究所，博士。

研究方向：主要从事植物系统学、进化发育生物学和调控基因组学研究。

doi: https://doi.org/10.1038/s41467-020-15658-2

Journal: Nature Communications

Published date: April 14, 2020

p.s. 通讯往期文章链接：

Nature Plants：植物花多样化背后潜在发育机制(综述)

蜜腺相关研究链接：

Plant Cell：矮牵牛与拟南芥蜜腺发育的分子基础

Plant Cell：矮牵牛与拟南芥的蜜腺特化