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Research Project: Genetic Improvement of Citrus for Enhanced Resistance to Huanglongbing Disease and Other Stresses

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Title: Identification of citrus immune regulators involved in defence against Huanglongbing using a new functional screening system

Author
item HUANG, CHIEN Y - University Of California
item NIU, DONGDONG - University Of California
item KUND, GREGORY - University Of California
item JONES, MIKE - University Of California
item ALBRECHT, UTE - University Of Florida
item NGUYEN, LINCOLN - University Of California
item BUI, CHRISTINE - University Of California
item RAMADUGU, CHANDRIKA - University Of California
item Bowman, Kim
item TRUMBLE, JOHN - University Of California
item JIN, HAILING - University Of California

Submitted to: Plant Biotechnology Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/18/2020
Publication Date: 10/27/2020
Citation: Huang, C., Niu, D., Kund, G., Jones, M., Albrecht, U., Nguyen, L., Bui, C., Ramadugu, C., Bowman, K.D., Trumble, J., Jin, H. 2020. Identification of citrus immune regulators involved in defence against Huanglongbing using a new functional screening system. Plant Biotechnology Journal. 19(4):757-766. https://doi.org/10.1111/pbi.13502.
DOI: https://doi.org/10.1111/pbi.13502

Interpretive Summary: Huanglongbing (HLB) is a devastating disease of citrus, and there are currently few commercial citrus varieties with useful tolerance and very few useful management strategies to control the disease. HLB-tolerance has been identified in some citrus relatives and citrus hybrids, but introgression of this tolerance in citrus and work with defense regulators is difficult because of the very long life-cycle and limited opportunities for genetic recombination in citrus. A novel and rapid functional screening method was developed using a closely related virus/vector/host system based on potato, which can be used to rapidly identify plant defense regulators against the disease in citrus. These defense regulators can then be used as tools in citrus to more rapidly develop tolerant and resistant varieties, and to study the pathogen system.

Technical Abstract: Huanglongbing (HLB) is the most devastating citrus disease in the world. Almost all commercial citrus varieties are susceptible to the causal bacterium Candidatus Liberibacter asiaticus (CLas), which is transmitted by the Asian citrus psyllid (ACP). Currently, there are no efficient management strategies to control HLB. HLB-tolerant traits have been reported in some citrus relatives and citrus hybrids, which offer a direct pathway for discovering natural defense regulators to combat HLB. Through comparative analysis of small Ribonucleic acid (RNA) profiles and target gene expression of a HLB-tolerant citrus hybrid and a susceptible citrus variety, we identified a panel of candidate regulators for HLB-tolerance. These regulators display similar expression patterns in two HLB-tolerant citrus relatives with distinct geographic and genetic backgrounds. Because the functional validation of candidate regulators in tree crops is challenging, we developed a novel rapid functional screening method, using a Candidatus Liberibacter solanacearum (CLso)/potato psyllid/ Nicotiana benthamiana interaction system to mimic the natural transmission and infection circuit of the HLB complex. When combined with virus-induced gene silencing, this innovative cost-effective method allows rapid functional identification of plant defense regulators against CLas.