Spatial chemistry of citrus reveals molecules bactericidal to Candidatus Liberibacter asiaticus

Authors: AKSENOV, ALEXANDER - University Of Connecticut; BLACUTT, ALEX - University Of California, Riverside; GINNAN, NICHOLE - Pennsylvania State University; ROLSHAUSEN, PHILIPPE - University Of California, Riverside; MELNIK, ALEXEY - University Of Connecticut; LOTFI, ALI - University Of Connecticut; GENTRY, EMILY - Virginia Tech; RAMASAMY, MANIKANDAN - Texas A&M University; McCollum, Thomas; ZUNIGA, CRISTAL - University Of California, San Diego; ZENGLER, KARSTEN - University Of California, San Diego; MANDADI, KRANTHI - Texas A&M University; DORRESTEIN, PIETER - University Of California, San Diego; ROPER, CAROLINE - University Of California, Riverside

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/16/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: Huanglongbing (HLB), associated with the psyllid-vectored phloem-limited bacterium, Candidatus Liberibacter asiaticus (CLas), is a threat to all citrus production worldwide and has had a severe impact on the Florida citrus industry. There are currently no cures or treatments available for this disease. Through a series of chemical and structural change experiments, it was determined that flavanoid biosynthesis was disrupted in infected citrus trees and that CLas converts an important chemical precursor to a new compound that blocks antibacterial activity. Using in vitro bioassays, we demonstrated that ferulic acid and bioflavonoids are indeed highly bactericidal to CLas, with the activity on par with a reference antibiotic, oxytetracycline, which is approved for HLB management. These compounds are currently being evaluated as therapeutic alternatives to antibiotics for HLB treatment.

Technical Abstract: Huanglongbing (HLB), associated with the psyllid-vectored phloem-limited bacterium, Candidatus Liberibacter asiaticus (CLas), is a disease threat to all citrus production worldwide. Currently, there are no sustainable curative or prophylactic treatments available. In this study, we utilized mass spectrometry (MS)-based metabolomics in combination with 3D molecular mapping to visualize complex chemistries within plant tissues to explore how these chemistries change in vivoin vivo in HLB-infected trees. We demonstrate how spatial information from molecular maps of branches and single leaves yields insight into the biology not accessible otherwise. In particular, we found evidence that flavonoid biosynthesis is disrupted in HLB-infected trees, and an increase in the polyamine, feruloylputrescine, is highly correlated with an increase in disease severity. Based on mechanistic details revealed by these molecular maps, followed by metabolic modeling, we formulated and tested the hypothesis that CLas infection either directly or indirectly converts the precursor compound, ferulic acid, to feruloylputrescine to suppress the antimicrobial effects of ferulic acid and biosynthetically downstream flavonoids. Using in vitro bioassays, we demonstrated that ferulic acid and bioflavonoids are indeed highly bactericidal to CLas, with the activity on par with a reference antibiotic, oxytetracycline, recently approved for HLB management. We propose these compounds should be evaluated as therapeutics alternatives to the antibiotics for HLB treatment. Overall, the utilized 3D metabolic mapping approach provides a promising methodological framework to identify pathogen-specific inhibitory compounds in planta for potential prophylactic or therapeutic applications.