Citrus Huanglongbing (HLB) is one of the most destructive citrus diseases worldwide, mainly caused by ‘ Liberibacter asiaticus’ (Las). HLB plants commonly present zinc deficiency chlorosis, which is evidenced with decreased zinc content and upregulation of genes encoding zinc transport proteins (ZIPs). However, the mechanism of how ZIPs are activated in response to Las infection is unknown. Herein, the phylogenetic analysis was done for ZIPs and its potential upstream regulator bZIPs on the genome-wide level. Fifty-six bZIP transcription factor members classified into thirteen groups and twelve ZIP members were identified from . CsbZIP23 and CsbZIP24 harboring Zinc-sensor motif (ZSM) were characterized as the homologues of bZIP19/23 in regulation of zinc homeostasis, and both were highly expressed in leaves compared to stems and roots. CsbZIP24 was further demonstrated in activation of gene expression by binding to its promoter containing Zinc Deficiency Response Elements (ZDRE) rather than CsbZIP23. Additionally, the induction of both and was observed in HLB diseased plants. Taken together, zinc sensor members were firstly identified in citrus and CsbZIP24 was proposed as the key factor in regulation of gene expression to accommodate zinc-deficient conditions that caused by Las colonization.

中文翻译：

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柑橘bZIP家族基因鉴定分析及CsbZIP24在黄龙病应答中的作用


柑橘黄龙病（HLB）是世界范围内最具破坏性的柑橘病害之一，主要由‘亚洲利伯里杆菌’（Las）引起。 HLB 植物通常会出现缺锌黄化，这可以通过锌含量降低和编码锌转运蛋白 (ZIP) 的基因上调来证明。然而，ZIP 如何响应 Las 感染而被激活的机制尚不清楚。在此，我们在全基因组水平上对 ZIP 及其潜在上游调节因子 bZIP 进行了系统发育分析。从 中鉴定出 56 个 bZIP 转录因子成员，分为 13 个组和 12 个 ZIP 成员。含有锌传感器基序（ZSM）的 CsbZIP23 和 CsbZIP24 被认为是调节锌稳态的 bZIP19/23 的同源物，并且与茎和根相比，两者在叶中高表达。 CsbZIP24 通过结合其含有缺锌反应元件 (ZDRE) 的启动子而不是 CsbZIP23，进一步证明了其在基因表达激活中的作用。此外，在 HLB 患病植物中观察到了 和 的诱导。总而言之，锌传感器成员首先在柑橘中被发现，并且 CsbZIP24 被认为是调节基因表达的关键因子，以适应 Las 定植引起的缺锌条件。