Although plant diseases generally cause more severe symptoms under conditions of high temperature and high humidity(HTHH), how plant respond to pathogen attack under this condition remains elusive. As an example, we herein comparatively studied pepper(Capsicum annuum) immunity against Ralstonia solanacearum under HTHH and ambient temperature by approaches of reverse genetics. We found that pepper respond to R.solanacearum infection by activating salicylic-acid- and jasmonic-acid-mediated immunity at ambient temperature. Under HTHH, However, it no longer activates JA-mediated immunity and activates only transient SA signaling at the early stage of R.solanacearum infection, but instead induces cytokinin mediated immunity. These two immune systems are positively regulated by CaWRKY40 via binding the WT-box and a novel W-box like (WL) box, respectively, in an environment-dependent manner: CaWRKY40 is activated upon R. solanacearum infection under HTHH, thereby upregulating ISOPENTENYLTRANSFERASE5(IPT5). The resulting cytokinin then works synergistically with CaWRKY40 in activating a subset of glutathione S-transferase genes via chromatin activation and WL-box binding, but prevent CaWRKY40 from activating ISOCHORISMATE SYNTHASE1 (ICS1) or SA-/JA-dependent pathogenesis-related genes by chromatin inactivation or by blocking WT-box binding. These results highlight the specific pepper immune response to R. solanacearum infection under HTHH and its synergistic activation by CaWRKY40 and cytokinins.

中文翻译：

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针对辣椒中青枯菌感染的两种免疫系统之间的环境依赖性切换

尽管植物病害通常会在高温高湿（HTHH）的条件下引起更严重的症状，但是在这种条件下植物如何应对病原体的攻击仍然难以捉摸。例如，我们在HTHH和环境温度下通过逆向遗传学方法比较研究了辣椒对青枯雷尔氏菌的免疫力。我们发现辣椒在环境温度下会通过激活水杨酸和茉莉酸介导的免疫反应来响应茄形假单胞菌感染。然而，在HTHH的作用下，它不再激活JA介导的免疫，而仅在茄形支原体感染的早期激活瞬时的SA信号，而是诱导细胞分裂素介导的免疫。CaWRKY40通过结合WT-box和新型W-box like（WL）框来积极调节这两个免疫系统，CaWRKY40在HTHH下感染青枯菌后被激活，从而上调ISOPENTENYLTRANSFERASE5（IPT5）。然后，产生的细胞分裂素与CaWRKY40协同作用，通过染色质激活和WL-box结合激活谷胱甘肽S-转移酶基因的一个子集，但通过染色质阻止CaWRKY40激活ISOCHORISMATE SYNTHASE1（ICS1）或SA- / JA依赖性发病相关基因激活或阻止WT-box绑定。这些结果突出了辣椒对HTHH感染青枯菌的特异性免疫反应，以及CaWRKY40和细胞分裂素的协同激活作用。然后，产生的细胞分裂素与CaWRKY40协同工作，通过染色质激活和WL-box结合激活谷胱甘肽S-转移酶基因的一个子集，但阻止CaWRKY40激活染色质引起的ISOCHORISMATE SYNTHASE1（ICS1）或SA- / JA依赖的发病相关基因激活或阻止WT-box绑定。这些结果突出了辣椒对HTHH感染青枯菌的特异性免疫反应，以及CaWRKY40和细胞分裂素的协同激活作用。然后，产生的细胞分裂素与CaWRKY40协同作用，通过染色质激活和WL-box结合激活谷胱甘肽S-转移酶基因的一个子集，但通过染色质阻止CaWRKY40激活ISOCHORISMATE SYNTHASE1（ICS1）或SA- / JA依赖性发病相关基因激活或阻止WT-box绑定。这些结果突出了辣椒对HTHH感染青枯菌的特异性免疫反应，以及CaWRKY40和细胞分裂素的协同激活作用。