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ARS Home » Southeast Area » Fort Pierce, Florida » U.S. Horticultural Research Laboratory » Citrus and Other Subtropical Products Research » Research » Publications at this Location » Publication #322943
Title: Molecular responses to small regulating molecules against Huanglongbing disease

Author
item MARTINELLI, FEDERICO - Universita Degli Studi Di Salerno
item DOLAN, DAVID - University Of California
item FILECCIA, VERONICA - Universita Degli Studi Di Salerno
item REAGAN, RUSSELL - University Of California
item PHU, MY - University Of California
item SPANN, TIMOTHY - University Of Florida
item McCollum, Thomas
item DANDEKAR, ABHAYA - University Of California

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/6/2016
Publication Date: 7/26/2016
Citation: Martinelli, F., Dolan, D., Fileccia, V., Reagan, R., Phu, M., Spann, T., Mccollum, T.G., Dandekar, A. 2016. Molecular responses to small regulating molecules against Huanglongbing disease. PLoS One. 11(7):e0159610. doi:10.1371/journal.pone.0159610.

Interpretive Summary: Huanglongbing (HLB; citrus greening) is the most devastating disease of citrus worldwide. The Florida citrus industry has been devastated by HLB, the Texas citrus industry is also being affected, and the threat to the California citrus industry is serious. To date, there is no cure available for HLB, once trees begin to express symptoms of the disease, decline progresses until the trees are no longer economically viable. In this work, we compared different combinations of organic compounds were tested for the ability to modulate citrus molecular responses to infection with Candidatus Liberibacter asiaticus, presumed causal agent of HLB disease. Three therapeutic solutions with one or more compounds were tested: 1) L-arginine, 2) 6-benzyl-adenine combined with gibberellins, and 3) sucrose combined with atrazine. Each treatment contained K-phite mineral solution and was tested at two different concentrations. Two trials were conducted: one in the greenhouse and the other in the orchard. In the greenhouse study, 42 key genes involved in sugar and starch metabolism, hormone-related pathways, biotic stress responses, and secondary metabolism were analyzed on treated mature leaves and compared with untreated controls. Atrazine combined with sucrose mainly upregulated key genes involved in carbohydrate metabolism such as sucrose-phosphate synthase, sucrose synthase, starch synthase, and alpha-amylase. Atrazine also affected expression of some key genes involved in plant responses to infection. Plant growth regulators Benzyladenine and gibberellins enhanced two important genes involved in biotic stress responses. Several treatments upregulated NPR1 and HSP82 genes which might help protect protein folding and integrity. Some key genes were chosen as biomarkers to analyze molecular responses to treatments under field conditions. GPT2 was downregulated by all therapeutic treatments. Arginine-induced genes involved in systemic acquired resistance included PR1, WRKY70, and EDS1. Our data suggest that long-term application of treatments that combine these regulating molecules may slow the rate of decline in HLB-affected trees.

Technical Abstract: Huanglongbing (HLB; citrus greening) is still the most devastating disease of citrus worldwide. No cure is yet available for this disease and trees generally decline from infections after several months. Disease management still depends on early detection of symptoms and chemical control of insect vectors. In this work, different combinations of organic compounds were tested for the ability to modulate citrus molecular responses to HLB disease beneficially. Three therapeutic solutions with one or more compounds were tested: 1) L-arginine, 2) 6-benzyl-adenine combined with gibberellins, and 3) sucrose combined with atrazine. Each treatment contained K-phite mineral solution and was tested at two different concentrations. Two trials were conducted: one in the greenhouse and the other in the orchard. In the greenhouse study, 42 key genes involved in sugar and starch metabolism, hormone-related pathways, biotic stress responses, and secondary metabolism were analyzed on treated mature leaves and compared with untreated controls. Atrazine combined with sucrose mainly upregulated key genes involved in carbohydrate metabolism such as sucrose-phosphate synthase, sucrose synthase, starch synthase, and -amylase. Atrazine also affected expression of some key genes involved in systemic acquired resistance such as EDS1, TGA6, WRKY33, and MYC2. Benzyladenine and gibberellins enhanced two important genes involved in biotic stress responses: WRKY54 and WRKY59. TGA5 was significantly induced by arginine. Several treatments upregulated NPR1 and HSP82, which might help protect protein folding and integrity. Some key genes were chosen as biomarkers to analyze molecular responses to treatments under field conditions. GPT2 was downregulated by all therapeutic treatments. Arginine-induced genes involved in systemic acquired resistance included PR1, WRKY70, and EDS1. These molecular data encourage long-term application of treatments that combine these regulating molecules in field trials.