Morphological studies of rose prickles provide new insights

Zhou et al. Horticulture Research (2021)8:221 https://doi.org/10.1038/s41438-021-00689-7 ARTICLE Horticulture Research www.nature.com/hortres Open Access Morphological studies of rose prickles provide new insights 1234567890():,; 1234567890():,; 1234567890():,; 1234567890():,; Ningning Zhou1,2 ✉, Fabienne Simonneau3, Tatiana Thouroude1, Laurence Hibrand-Saint Oyant1 and Fabrice Foucher1 ✉ Abstract Prickles are common structures in plants that play a key role in defense against herbivores. In the Rosa genus, prickles are widely present with great diversity in terms of form and density. For cut rose production, prickles represent an important issue, as they can damage the flower and injure workers. Our objectives were to precisely describe the types of prickles that exist in roses, their tissues of origin and their development. We performed a detailed histological analysis of prickle initiation and development in a rose F1 population. Based on the prickle investigation of 110 roses, we proposed the first categorization of prickles in the Rosa genus. They are mainly divided into two categories, nonglandular prickles (NGPs) and glandular prickles (GPs), and subcategories were defined based on the presence/ absence of hairs and branches. We demonstrated that NGPs and GPs both originate from multiple cells of the ground meristem beneath the protoderm. For GPs, the gland cells originate from the protoderm of the GP at the early developmental stage. Our findings clearly demonstrate that prickles are not modified trichomes (which originate from the protoderm). These conclusions are different from the current mainstream hypothesis. These results provide a foundation for further studies on prickle initiation and development in plants. Introduction Superficial tissues (epidermis) and appendage structures (trichomes, spinescences) of plant organs are the first lines of defense against multiple abiotic and biotic stresses. The basic terminologies of these appendages are frequently inaccurately cited in scientific reports, leading to confusion and difficulties in distinguishing the different terms. Some authors have described emergences as prickles, e.g., prickles on the stems or leaves of plants such as Solatium torvium, Aiphanes acanthophylla, and roses1, and some have referred to trichomes as emergences, e.g., grape emergences2. Another common Correspondence: Ningning Zhou () or Fabrice Foucher () 1 Univ Angers, Institut Agro, INRAE, IRHS, SFR QUASAV, F-49000 Angers, France 2 National Engineering Research Center for Ornamental Horticulture; Flower Research Institute (FRI), Yunnan Academy of Agricultural Sciences, Kunming 650231, China Full list of author information is available at the end of the article These authors contributed equally: Laurence Hibrand-Saint Oyant, Fabrice Foucher source of confusion originates among prickles, thorns, and spines. Many plants described with thorns or spines actually have prickles3–8. Depending on the presence of vascular bundles, we can divide these structures into two categories: (1) trichomes (Supplementary Fig. 1a and b) and prickles (Supplementary Fig. 1c and d), which are not vascularized and are generally easy to remove9,10; and (2) thorns (Supplementary Fig. 1e and f) and spines (Supplementary Fig. 1g), which have vascular bundles and cannot be easily separated from organs that have vascular tissues (spines, usually modified from leaves, and thorns, modified from stems or shoots) (Supplementary Fig. 1h)11,12. Thus, prickles can be easily distinguished from thorns and spines: mature prickles are outgrowths connected to the bark13, while thorns and spines are outgrowths connected to the phloem and the xylem11,14. Confusion of trichomes and prickles is also common. Trichomes are epidermal appendages that originate only from the protoderm, and they are diverse according to © The Author(s) 2021 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 license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license 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 license, visit http://creativecommons.org/licenses/by/4.0/. Zhou et al. Horticulture Research (2021)8:221 their final forms and structures, locations, and functions10,15. They are mainly divided into nonglandular trichomes (NGTs) and glandular trichomes (GTs)10. Both types can be unicellular or multicellular and branched or unbranched. Presently, the genetic and molecular mechanisms of NGTs are well understood in Arabidopsis thaliana, and numerous related genes have been identified (reviewed by Hülskamp16 and Zhou17). These genes encode proteins belonging to the MYB, bHLH, WD40, WRKY, and C2H2 zinc finger protein families. A trimeric activator complex consisting of MYB (GLABRA1)-bHLH (GLABROUS3/ENHANCER OF GL3)-WDR (TRANSPARENT TESTA GL1) plays a key role in NGT initiation16. The genetic pathway for GT initiation is not yet well known (reviewed by Huchelmann et al.18 and Chalvin et al.19). In Solanum, an HD-ZIP IV transcription factor (WOOLLY) may interact with the B-type cyclin CycB2 and the C2H2 zinc-finger protein (HAIR) to induce GT initiation (reviewed by Chalvin et al.19). In Artemisia annua, an HD-ZIP IV transcription factor (AaHD8) may interact with a MIXTA-like protein (AaMIXTA1), which activates AaHD1, leading to GT initiation20. Prickles are common structures in plants, which are involved in defense against insects and large mammalian herbivores21. The morphogenetic and molecular mechanisms underlying prickle initiation and development remain largely unknown. A few reports have described the anatomical structures of prickles13, especially in roses9,22,23. As the analyses were performed in late developmental stages, conclusions about the tissues from which prickles originate are difficult to draw, leading to different and controversial hypotheses developed below. The mainstream hypothesis is that prickles originate from multiple cellular divisions of the epidermis3,24,25 and are considered as modified GTs, with lignification leading to a hard and sharp appendage2,5,22,26. Nonglandular prickles (NGPs) were described as a late stage of glandular prickles (GPs)22. Based on this hypothesis, molecular approaches were developed to test the trichome origin of prickles in rose and Rubus. A comparison of transcript accumulation between rose F1 genotypes with no, lowdensity (NGPs (...truncated)