Effects of application of (Z)-3-Hexenol on Solanum lycopersicum

The economic losses caused by plant stresses and the greater awareness of the environment sustainability make evident the need to develop new agricultural strategies. The identification of natural compounds participating in the plant defence signalling that can be used as inducers of the defensive response constitutes one of these strategies. To this purpose, I2Tom.Com aims to study the Tomato signalling defence response against bacteria which is activated both within the plant upon infection, through the production of mobile signals (Intra-plant Communication), and in the neighbouring plants, through the perception by the receiving plants (r-plants) of volatile signals released by infected emitting plants (e-plants; Inter-plant Communication). Particularly, we will explore the involvement in these signalling mechanisms of three groups of molecules participating in the tomato response against bacteria, including the benzenoids salicylic acid (SA) and its methyl-ester (MeSA), hydroxylated monoterpenoids, and esters of green leaf volatiles (GLVs). Our proposal is based on our results on the identification of volatile organic compounds (VOCs) differentially emitted by tomato plants that effectively resist the bacterial infection, including esters of GLVs and hydroxylated monoterpenoids. We have also demonstrated the defensive role for a Z-3-hexenyl butyrate (HB), a GLV ester that has been patented and licenced because of its extraordinary capacity to induce the stomata closure, displaying multiple uses in agriculture (Lison et al., 2017; Lopez-Gresa et al, 2018; Paya et al., 2020). Besides, some preliminary results on the defensive role of hydroxylated monoterpenoids are included in the state of the art support our proposal. Related to the defensive phytohormone SA, our aim also arises from some unpublished results in our group on the role of a putative salicylate 5-hydroxylase (Sl S5H) that hydroxylates SA (2-hydroxybenzoic acid) into gentisic acid (GA, 2,5-dihydroxybenzoic acid). We have observed that silencing Sl_S5H noticeably enhances resistance to bacteria in tomato plants, pointing out the importance of SA catabolism in the plant signalling response. Since SA can be methylated into the volatile form MeSA, these transgenic plants constitute an excellent tool to study the role of this phenolic compound not only in the intra- but also in the inter-plant defensive communication against bacteria or other pathogens. On the other hand, our group has recently unravelled the ribosomal stress as a new dimension of the viroid pathogenesis (Cottilli et al, 2019; Prol et al., 2020). Therefore, this phenomenon will also be explored in these transgenic plants upon viroid infection. Mostly, I2Tom.Com aims to study the role of three families of compounds on the tomato defence response through the phenotypical, molecular and chemical characterization of: (i) transgenic e-plants with alterations in the production of any of these defensive signals, and (ii) r-plants grown in the presence or absence of these e-plants specifically emitting different aromas for resistance. Our proposal will help understand the plant signalling defence response that could lead to the development of new biotechnological alternatives to combat biotic stresses in agriculture, through the identification of new natural inducers and the generation of transgenic plants over-emitting them.

植物胁迫引发的经济损失，叠加公众对环境可持续性的认知持续提升，均凸显出开发新型农业策略的迫切性。筛选可作为防御反应诱导剂、参与植物防御信号传导（plant defence signalling）的天然化合物，正是此类策略的核心方向之一。为此，I2Tom.Com项目旨在研究番茄抗细菌防御信号响应：该响应在植株受侵染后，通过产生移动信号激活（植株内通讯，Intra-plant Communication）；同时在邻近植株间，通过接收植株（r-plants）感知被侵染的释放植株（e-plants; 植株间通讯，Inter-plant Communication）释放的挥发性信号来启动。具体而言，本项目将探究三类参与番茄抗细菌防御反应的分子在上述信号传导机制中的调控作用，包括苯类化合物（benzenoids）水杨酸（salicylic acid, SA）及其甲酯（methyl ester, MeSA）、羟基化单萜类物质，以及绿叶挥发物酯类（green leaf volatiles, GLVs）。本项目的研究基础源于我们的前期成果：我们已鉴定出在抗细菌侵染的番茄植株中差异释放的挥发性有机化合物（volatile organic compounds, VOCs），其中涵盖GLVs酯类与羟基化单萜类物质。我们还证实了丁酸Z-3-己烯酯（Z-3-hexenyl butyrate, HB）——一种GLVs酯类——的防御功能：该物质因具备诱导气孔关闭的卓越能力已获得专利并完成授权，在农业领域具备多重应用价值（Lison et al., 2017; Lopez-Gresa et al, 2018; Paya et al., 2020）。此外，关于羟基化单萜类物质防御功能的部分预实验结果已发表于本领域前沿研究，可为本项目提供佐证。针对防御性植物激素（defensive phytohormone）SA，我们的研究目标还源于课题组内的部分未发表成果：一种推定的水杨酸5-羟化酶（salicylate 5-hydroxylase, Sl S5H）可将SA（2-羟基苯甲酸，2-hydroxybenzoic acid）羟化为龙胆酸（gentisic acid, GA, 2,5-二羟基苯甲酸）。我们观察到，沉默Sl_S5H基因可显著提升番茄植株的抗细菌能力，凸显出SA分解代谢在植物信号传导响应中的重要性。由于SA可被甲基化为挥发性形式MeSA，此类转基因植株（transgenic plants）成为绝佳的研究工具，可用于探究该酚类化合物（phenolic compound）在植物针对细菌或其他病原体的防御通讯中的作用——不仅涉及植株内通讯，还涵盖植株间通讯。另一方面，本课题组近期揭示了核糖体胁迫（ribosomal stress）作为类病毒致病机制（viroid pathogenesis）的全新维度（Cottilli et al, 2019; Prol et al., 2020）。因此，本项目也将在受类病毒侵染的转基因植株中探究此类现象。总体而言，I2Tom.Com项目旨在通过以下两类材料的表型、分子与化学表征，探究三类化合物在番茄防御反应中的作用：(i) 上述防御信号产生过程发生改变的转基因释放植株（e-plants）；(ii) 分别与这些特异性释放不同抗性相关挥发性气味的e-plants共培养、或单独培养的接收植株（r-plants）。本项目将助力解析植物防御信号传导响应，通过筛选新型天然诱导剂并培育过量释放此类物质的转基因植株，为农业领域对抗生物胁迫（biotic stresses）开发全新的生物技术解决方案。