Hexaacetyl-chitohexaose, a chitin-derived oligosaccharides, transiently activiates citrus defenses and alters the feeding behavior of asian citrus psyllid

Authors: SHI, QINGCHUN - Former ARS Employee; George, Justin; Krystel, Joseph; Zhang, Shujian; Lapointe, Stephen; STELINSKI, LUKAZ - University Of Florida; Stover, Eddie

Submitted to: Horticulture Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/23/2019
Publication Date: 6/8/2019
Citation: Shi, Q., George, J., Krystel, J.A., Zhang, S., Lapointe, S.L., Stelinski, L.L., Stover, E.W. 2019. Hexaacetyl-chitohexaose, a chitin-derived oligosaccharides, transiently activiates citrus defenses and alters the feeding behavior of asian citrus psyllid. Horticulture Research. 6(76):1-10. https://doi.org/10.1038/s41438-019-0158-y.
DOI: https://doi.org/10.1038/s41438-019-0158-y

Interpretive Summary: Citrus Huanglongbing (HLB) is a devastating disease for US citrus industry. This bacterial disease is transmitted by the insect Asian citrus psyllid (ACP) and genetic bacterial resistance has been lacking in commercial citrus types. This renders citrus resistance to the insect vector an important element for the disease management. This study showed chitin can activate citrus defense which in turn inhibit ACP feeding activities. However, this defense is transient under the experimental conditions and did not appear to alter ACP host selection behavior and mortality. Future studies may uncover if chitin-induced citrus defense can lead to meaningful insect resistance for the application in disease management.

Technical Abstract: Plants have a perception system triggered by pathogen and pest signals to initiate defense. These signals include evolutionarily conserved molecules from microbes and insects termed pathogen/herbivore-associated molecular patterns (PAMPs/HAMPs). Here we showed that chitin, a structural component in insect exoskeletons and fungi cell walls, upregulated defense-associated genes WRKY22, GST1, RAR1, EDS1, PAL1 and NPR2, and downregulated ICS1 at 1h after chitin treatment in Sun Chu Sha mandarin leaves. The effect was transient as defense gene transcriptional changes were not observed at 18 hours after the treatment. Electrical penetration graph (EPG) recordings were used to study the feeding behavior of Asian citrus psyllid (ACP) following the chitin treatment. ACP is the hemipteran vector of Candidatus Liberibacter asiaticus (CLas), the pathogen associated with huanglongbing (HLB). Adult ACP displayed reduced intercellular probing, reduced xylem feeding count and duration, and increased non-probing activity on chitin-treated citrus compared to controls. During an 18-hour recording, percentage for total duration of xylem ingestion, phloem ingestion, intercellular probing were lower, and the percentage of non-probing behavior was higher in chitin treated leaves than in controls. In host selection behavior studies, chitin treatment did not alter the attractiveness of citrus leaves under light or dark conditions. Additionally, ACP feeding on chitin-treated leaves did not show differences in mortality for up to 10 day of exposure. In summary, we report that chitin induced a transient defense in citrus that had an inhibitory effect on ACP feeding but did not affect host selection or the insect fitness under the tested conditions.