RT Journal Article SR Electronic T1 Citrus Huanglongbing is an immune-mediated disease that can be treated by mitigating reactive oxygen species triggered cell death of the phloem tissues caused by Candidatus Liberibacter asiaticus JF bioRxiv FD Cold Spring Harbor Laboratory SP 2021.08.15.456409 DO 10.1101/2021.08.15.456409 A1 Wenxiu Ma A1 Zhiqian Pang A1 Xiaoen Huang A1 Sheo Shankar Pandey A1 Jinyun Li A1 Jin Xu A1 Diann S. Achor A1 Fernanda N.C. Vasconcelos A1 Connor Hendrich A1 Yixiao Huang A1 Wenting Wang A1 Donghwan Lee A1 Nian Wang YR 2021 UL http://biorxiv.org/content/early/2021/08/24/2021.08.15.456409.abstract AB The immune system is critical for keeping animals and plants healthy from pathogens. However, immune-mediated diseases are also common for human. Immune-mediated diseases have not been reported for plants. Here, we present evidence that citrus Huanglongbing (HLB), caused by phloem-colonizing Candidatus Liberibacter asiaticus (CLas), is an immune-mediated disease. CLas infection of Citrus sinensis stimulated systemic and chronic immune response in the phloem tissues including reactive oxygen species (ROS) production as indicated by H2O2, callose deposition, and induction of immune related genes. Systemic cell death of companion and sieve element cells, but not surrounding parenchyma cells, was observed following ROS production triggered by CLas. ROS production triggered by CLas localized in phloem tissues. The H2O2 concentration in exudates extracted from phloem enriched bark tissue of CLas infected plants reached a threshold of killing citrus protoplast cells, which was suppressed by uric acid (a ROS scavenger) and gibberellin. Foliar spray of HLB positive citrus with antioxidants (uric acid and rutin) and gibberellin significantly reduced both H2O2 concentrations and cell death in phloem tissues induced by CLas and reduced HLB symptoms. RNA-seq analyses of CLas infected and health C. sinensis support that CLas causes oxidative stress. In sum, HLB is an immune-mediated disease and both mitigating ROS via antioxidants and promoting plant growth can reduce cell death of the phloem tissues caused by CLas, thus controlling HLB.Competing Interest StatementThe authors have declared no competing interest.