Journal Article

Citrus Huanglongbing is a pathogen-triggered immune disease that can be mitigated with antioxidants and gibberellin

Pang, Zhiqian, Li, Jinyun, Pandey, Sheo Shankar, Huang, Xiaoen, Vasconcelos, Fernanda N. C., Huang, Yixiao, Ma, Wenxiu, Stanton, Daniel, Xu, Jin, Lee, Donghwan, Achor, Diann S., Wang, Wenting, Hendrich, Connor, Wang, Nian

2022

Overview

Huanglongbing (HLB) is a devastating disease of citrus, caused by the phloem-colonizing bacterium Candidatus Liberibacter asiaticus (CLas). Here, we present evidence that HLB is an immune-mediated disease. We show that CLas infection of Citrus sinensis stimulates systemic and chronic immune responses in phloem tissue, including callose deposition, production of reactive oxygen species (ROS) such as H 2 O 2 , and induction of immunity-related genes. The infection also upregulates genes encoding ROS-producing NADPH oxidases, and downregulates antioxidant enzyme genes, supporting that CLas causes oxidative stress. CLas-triggered ROS production localizes in phloem-enriched bark tissue and is followed by systemic cell death of companion and sieve element cells. Inhibition of ROS levels in CLas-positive stems by NADPH oxidase inhibitor diphenyleneiodonium (DPI) indicates that NADPH oxidases contribute to CLas-triggered ROS production. To investigate potential treatments, we show that addition of the growth hormone gibberellin (known to have immunoregulatory activities) upregulates genes encoding H 2 O 2 -scavenging enzymes and downregulates NADPH oxidases. Furthermore, foliar spray of HLB-affected citrus with gibberellin or antioxidants (uric acid, rutin) reduces H 2 O 2 concentrations and cell death in phloem tissues and reduces HLB symptoms. Thus, our results indicate that HLB is an immune-mediated disease that can be mitigated with antioxidants and gibberellin. Huanglongbing is a devastating disease of citrus, caused by phloem-colonizing bacteria. Here, the authors present evidence that the disease is the result of an exacerbated immune response to the infection, including production of reactive oxygen species, and that antioxidants and a growth-promoting hormone can mitigate disease symptoms.

• Publisher: Nature Publishing Group UK,Nature Publishing Group,Nature Portfolio
• Subject: 14/19 / 14/63 / 45/91 / 631/326/41/2531 / 631/326/41/2533 / 631/326/421 / 631/449/2169/597 / Antioxidants / Antioxidants - metabolism / Antioxidants - pharmacology / Apoptosis / Bacteria / Bark / Candidatus Liberibacter asiaticus / Cell Death / Chronic infection / Citrus - immunology / Citrus - microbiology / Citrus fruits / Citrus sinensis / Disease control / Fruits / Genes / Gibberellins / Gibberellins - metabolism / Gibberellins - pharmacology / Glucans / Growth hormones / Host-Pathogen Interactions - immunology / Humanities and Social Sciences / Hydrogen peroxide / Hydrogen Peroxide - metabolism / Immune response / Immune system / Immune System Diseases / Immunological diseases / Immunoregulation / Infections / Liberibacter / multidisciplinary / NAD(P)H oxidase / Oxidation / Oxidative stress / Phloem / Plant bacterial diseases / Plant Diseases - immunology / Plant Diseases - microbiology / Reactive oxygen species / Rutin / Scavenging / Science / Science (multidisciplinary) / Signs and symptoms / Uric acid / Virulence