Longitudinal Transcriptomic, Proteomic, and Metabolomic Analysis of Citrus limon Response to Graft Inoculation by Candidatus Liberibacter asiaticus

Presymptomatic detection of citrus trees infected with ( Las), the bacterial pathogen associated with Huanglongbing (HLB; citrus greening disease), is critical to controlling the spread of the disease. To test whether infected citrus trees produce systemic signals that may be used for indirect disease detection, lemon ( ) plants were graft-inoculated with either Las-infected or control ( Las-) budwood, and leaf samples were longitudinally collected over 46 weeks and analyzed for plant changes associated with Las infection. RNA, protein, and metabolite samples extracted from leaves were analyzed using RNA-Seq, mass spectrometry, and H NMR spectroscopy, respectively. Significant differences in specific transcripts, proteins, and metabolites were observed between Las-infected and control plants as early as 2 weeks post graft (wpg). The most dramatic differences between the transcriptome and proteome of Las-infected and control plants were observed at 10 wpg, including coordinated increases in transcripts and proteins of citrus orthologs of known plant defense genes. This integrated approach to quantifying plant molecular changes in leaves of Las-infected plants supports the development of diagnostic technology for presymptomatic or early disease detection as part of efforts to control the spread of HLB into uninfected citrus groves.