Department of Plant Pathology, Citrus Research and Education Center, University of Florida, 700 Experiment Station Rd., Lake Alfred, FL 33850, U.S.A.
Department of Agricultural Botany, Faculty of Agriculture, Tanta University, Tanta, Egypt.
Mol Plant Microbe Interact. 2022 Mar;35(3):200-214. doi: 10.1094/MPMI-09-21-0241-R. Epub 2022 Mar 1.
Although the mitochondria retain all required enzymes for an intact tricarboxylic acid (TCA) cycle, plants might shift the cyclic flux from the TCA cycle to an alternative noncyclic pathway via -aminobutyric acid (GABA) shunt under specific physiological conditions. We hypothesize that several genes may ease this noncyclic flux and contribute to the citrus response to the phytopathogenic bacterium ' Liberibacter asiaticus', the causal agent of Huanglongbing in citrus. To test this hypothesis, we used multiomics techniques (metabolomics, fluxomics, and transcriptomics) to investigate the potential roles of putative homologies from Valencia sweet orange (). Our findings showed that ' L. asiaticus' significantly increased the endogenous GABA and succinate content but decreased ketoglutarate in infected citrus plants. Citrus genome harbors three putative genes, including amino-acid permease (also known as GABA permease; ), GABA transaminase (), and succinate-semialdehyde dehydrogenase (also known as GABA dehydrogenase; ). The transcript levels of , , and were upregulated in citrus leaves upon the infection with ' L. asiaticus' and after the exogenous application of GABA or deuterium-labeled GABA isotope (GABA-D). Moreover, our finding showed that exogenously applied GABA is quickly converted to succinate and fed into the TCA cycle. Likewise, the fluxomics study showed that GABA-D is rapidly metabolized to succinate-D. Our work proved that GABA shunt and three predicated genes from citrus, support the upstream noncyclic flux toward succinate rather than an intact TCA cycle and contribute to citrus defense responses to '. L. asiaticus'.[Formula: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.
尽管线粒体保留了完整三羧酸（TCA）循环所需的所有酶，但在特定生理条件下，植物可能通过 -氨基丁酸（GABA）分流将循环通量从 TCA 循环转移到替代的非循环途径。我们假设，在柑橘对植物病原菌 '亚洲韧皮杆菌'（引起黄龙病的原因）的反应中，几个基因可能会缓解这种非循环通量，并做出贡献。为了验证这一假设，我们使用多组学技术（代谢组学、通量组学和转录组学）来研究 Valencia 甜橙（）中假定同源物的潜在作用。我们的研究结果表明，'亚洲韧皮杆菌'显著增加了感染柑橘植物中的内源性 GABA 和琥珀酸含量，但降低了酮戊二酸含量。柑橘基因组含有三个假定的 基因，包括氨基酸渗透酶（也称为 GABA 渗透酶；）、GABA 转氨酶（）和琥珀酸半醛脱氢酶（也称为 GABA 脱氢酶；）。感染 '亚洲韧皮杆菌'后和外源施用 GABA 或氘标记 GABA 同位素（GABA-D）后，柑橘叶片中 、 和 的转录水平上调。此外，我们的研究结果表明，外源施用的 GABA 迅速转化为琥珀酸并进入 TCA 循环。同样，通量组学研究表明，GABA-D 迅速代谢为琥珀酸-D。我们的工作证明，GABA 分流和来自柑橘的三个预测的 基因支持上游非循环通量朝向琥珀酸，而不是完整的 TCA 循环，并有助于柑橘对 '亚洲韧皮杆菌'的防御反应。[公式：见正文]版权所有 2022 作者。这是一个在 CC BY-NC-ND 4.0 国际许可下发布的开放获取文章。
