1H NMR based metabolomics of Citrus sinensis leaves in response to Diaphorina citri infestation and Huanglongbing disease

Huanglongbing (HLB) is a fatal citrus disease currently threatening all
commercially relevant citrus varieties worldwide. In the United States,
the putative causative agent, Candidatus Liberibacter asiaticus (CLas), is
transmitted by the vector Diaphorina citri, commonly known as the Asian
citrus psyllid (ACP). Progress towards understanding CLas and its role in
HLB has been hindered by the inability to culture the bacterium and the
inability to confidently detect it in diseased trees during the
asymptomatic stage. To identify early changes in citrus metabolism in
response to inoculation of CLas using its natural psyllid vector, leaves
from Madam Vinous sweet orange (Citrus sinensis (L.) Osbeck) trees were
exposed to CLas-positive ACP or CLas-negative ACP and longitudinally
analyzed using transcriptomics (RNA sequencing), proteomics (liquid
chromatography-tandem mass spectrometry), and metabolomics (proton nuclear
magnetic resonance). At 4 weeks post-exposure (wpe) to psyllids, the
initial HLB plant response was primarily to the ACP and, to a lesser
extent, the presence or absence of CLas. Additionally, analysis of 4, 8,
12, and 16 wpe identified 17 genes that were consistently differentially
expressed between leaves exposed to CLas-positive ACP versus CLas-negative
ACP, one differentially abundant protein, and no differentially
accumulated metabolites. The results of this study inform identification
of early detection molecular targets and contribute to the broader
understanding of vector-transmitted plant pathogen interactions.