Location: Subtropical Plant Pathology ResearchTitle: 'Candidatus Liberibacter asiaticus' SED1 effector induces Huanglongbing chlorosis by downregulating host DDX3 gene
|LI, YANJIAO - Fujian Agricultural & Forestry University|
|ZHOU, YINGHUI - Fujian Agricultural & Forestry University|
|LIU, ZHIQIN - Fujian Agricultural & Forestry University|
|ZHUO, TAO - Fujian Agricultural & Forestry University|
|FAN, XIAOJING - Fujian Agricultural & Forestry University|
|ZOU, HUASONG - Fujian Agricultural & Forestry University|
Submitted to: International Journal of Molecular Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/25/2020
Publication Date: 10/27/2020
Citation: Li, Y., Zhou, Y., Liu, Z., Zhuo, T., Fan, X., Duan, Y., Zou, H. 2020. 'Candidatus Liberibacter asiaticus' SED1 effector induces Huanglongbing chlorosis by downregulating host DDX3 gene. International Journal of Molecular Sciences. 21(7996):1-13. https://doi.org/10.3390/ijms21217996.
Interpretive Summary: Citrus Huanglongbing (HLB), also known as citrus greening, is one of the most devastating citrus diseases, causing severe losses in worldwide citrus production. This disease is associated with three species of phloem-limited pathogenic bacteria: Candidatus Liberibacter asiaticus (Las), Candidatus Liberibacter africanus, and Candidatus Liberibacter americanus. Beside citrus, Las also infects several experimental plants, such as the model plant, Nicotiana benthamiana. In this study, we investigated the molecular mechanism underlying SDE1-mediated host plant responses. We found that host DEAD-box RNA helicase DDX3 was targeted by SDE1, and that downregulation of host DDX3 gene was associated with leaf chlorosis. These findings facilitate our understanding on Las pathogenesis and HLB symptom development. The CsDDX3 gene may serve as a critical target for gene editing to interfere citrus host susceptibility.
Technical Abstract: ‘Candidatus Liberibacter asiaticus’ (CLas) is the pathogenic bacterium that causes the disease Huanglongbing (HLB) in citrus and some model plants, such as Nicotiana benthamiana. After infection, CLas releases a set of effectors to modulate host responses. One of these critical effectors is Sec-delivered effector 1 (SDE1), which induces chlorosis and cell death in N. benthamiana. In this study, we revealed the DEAD-box RNA helicase (DDX3) interacts with SDE1. Gene silencing study revealed that knockdown of the NbDDX3 gene triggers leaf chlorosis, mimicking the primary symptom of CLas infection in N. benthamiana. The interactions between SDE1 and NbDDX3 were localized in the cell membrane. Overexpression of SDE1 resulted in suppression of NbDDX3 gene expression in N. benthamiana, which suggests a critical role of SDE1 in modulating NbDDX3 expression. Furthermore, we verified the interaction of SDE1 with citrus DDX3 (CsDDX3), and demonstrated that the expression of the CsDDX3 gene was significantly reduced in HLB-affected yellowing and mottled leaves of citrus. Thus, we provide molecular evidence that the downregulation of the host DDX3 gene is a crucial mechanism of leaf chlorosis in HLB-affected plants. The identification of CsDDX3 as a critical target of SDE1 and its association with HLB symptom development indicates that the DDX3 gene is an important target for gene editing, to interrupt the interaction between DDX3 and SDE1, and therefore interfere host susceptibility.