Extrafloral nectary–the sleeping beauty of plant science COMMENT Open Access Extrafloral nectary–the sleeping beauty of plant science CHEN Xiaoya Abstract Cotton is one of the most important cash crops, its growth season coincides with a high incidence of diverse groups of pests, leading to heavy use of pesticides. Recent identification of a signaling protein as a candidate regulator of cotton extrafloral nectary provides a new insight into the formation of sophisticated defense mechanisms in plants. Keywords: Extrafloral nectary, PB1 domain, GaNEC1I, Cotton, Gossypium, Indirect defense, Insect Main text Extrafloral nectary is an indirect defense device of plants and can be located on the shoot, leaf stalks, leaf blades or stipules, or on the inner or outer surfaces of the sepals but not involved in pollination (Heil 2011). However, its formation in crops and potential role in biocontrol of pests and diseases are under studied (Stenberg et al. 2015). Nectar, a sweet aqueous secretion consisting of sugars, amino acids and secondary me- tabolites, mediates the interactions of plants with pollinators and defenders (Heil 2011). More than 100 angiosperm species including cotton (Gossypium spp.) produce extrafloral nectar- ies to attract mutualistic animals to catch herbivores. The ex- ists of extrafloral nectarines in cotton speices are slightly different, since G. gossypiodes (D6) and allotertraploid G. tomentosum (AD3) have no nectarines on the midribs of leaves (Hu et al. 2020). Cotton accessions with variations in extrafloral nectaries, combined with the progresses in cotton genomics (Li et al. 2015; Hu et al. 2015; Li et al. 2017; Du et al. 2018; Ma et al. 2018; Yang et al. 2019; Yang et al. 2020; Zhang et al. 2015) provide an unprecedented opportunity to elucidate the genetic basis of nectar formation and ecological functions. Recently, Li, Yang and colleagues from Institute of Cotton Research of Chinese Academy of Agricultural Sci- ences, identified the causal quantitative trait locus (QTL)/gene for the cotton extrafloral nectary and revealed the genomic differences in the causal QTL regions as well as the potential network regulating nectary formation (Hu et al. 2020). Uncov- ered molecular details about nectary formation could be ap- plied to molecular breeding of cultivars that confer pest- resistance via biological control. Through investigating the extrafloral distribution in 27 different species, Hu et al. found that the nectary was present in the common ancestor of Kokia and Gossy- pium. The nectariless trait was thus derived from natural mutation. Based on a core collection of 215 G. arboreum accessions, they compared the extrafloral nectary- bearing to the nectariless accessions and found a region of Chr12 showing strong differentiation and overlapping with the QTL region identified via genome-wide ana- lysis. They further narrowed the candidate genes to a 96 kb region using an F2 population, and validated GaNEC1, encoding a Phox-Bem1 (PB1) domain- containing protein, as a regulator of nectary formation. They found that a deletion of five amino acids, together with a nonsynonymous substitution, probably caused structural alteration in the GaNEC1 protein and confer the nectariless phenotype. Silencing of GaNEC1 led to a smaller foliar nectary phenotype. Further, they found that the jasmonate (JA) related genes were up-regulated and the cell wall genes were down-regulated in the nec- tary. They also performed metabolomics analysis of the nectary secretion and identified more than 400 nectar components, including the expected saccharides and amino acids. © The Author(s). 2020 Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. Correspondence: xychen@sibs.ac.cn CAS Center for Excellence in Molecular Plant Sciences/Shanghai Institute of Plant Physiology and Ecology, Chinese Academy of Sciences, 300 Fenglin Road, Shanghai 200032, China Journal of Cotton ResearchCHEN Journal of Cotton Research (2020) 3:7 https://doi.org/10.1186/s42397-020-00051-7 http://crossmark.crossref.org/dialog/?doi=10.1186/s42397-020-00051-7&domain=pdf http://creativecommons.org/licenses/by/4.0/ mailto:xychen@sibs.ac.cn The PB1 domain is conserved in eukaryotes and modu- lates protein interactions. Identification of a PB1 domain- containing protein as a regulatory component of the extra- floral nectary formation and sheds a light on the molecular mechanism underlying the evolution and development of this adaptive sweet apparatus and can be an important pro- gress in this filed. Hopefully the finding will stimulate further investigation of various aspects of nectaries in flowers and other parts, which will help develop environmentally friendly, healthy and beautiful strategies for pests control. Acknowledgments The author thanks Dr. LIU Ningjing and WANG Lingjian for critical reading of the manuscript. Author’s contributions CHEN XY prepared and wrote the manuscript. The author read and approved the final manuscript. Funding Not applicable. Availability of data and materials No other data related to this study is available at this time. Ethics approval and consent to participate Not applicable. Consent for publication Not applicable. Competing interests The authors declare that they have no competing interests. Received: 27 February 2020 Accepted: 12 March 2020 References Du X, Huang G, He S, et al. Resequencing of 243 diploid cotton accessions based on an updated a genome identifies the genetic basis of key agronomic traits. 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