Longitudinal Transcriptomic,\nProteomic, and Metabolomic\nAnalysis of Citrus limon Response to Graft Inoculation\nby Candidatus Liberibacter asiaticus

Presymptomatic detection of citrus\ntrees infected with Candidatus Liberibacter asiaticus (CLas),\nthe bacterial pathogen associated with Huanglongbing (HLB; citrus\ngreening disease), is critical to controlling the spread of the disease.\nTo test whether infected citrus trees produce systemic signals that\nmay be used for indirect disease detection, lemon (Citrus\nlimon) plants were graft-inoculated with either CLas-infected or control (CLas−) budwood,\nand leaf samples were longitudinally collected over 46 weeks and analyzed\nfor plant changes associated with CLas infection.\nRNA, protein, and metabolite samples extracted from leaves were analyzed\nusing RNA-Seq, mass spectrometry, and 1H NMR spectroscopy,\nrespectively. Significant differences in specific transcripts, proteins,\nand metabolites were observed between CLas-infected\nand control plants as early as 2 weeks post graft (wpg). The most\ndramatic differences between the transcriptome and proteome of CLas-infected and control plants were observed at 10 wpg,\nincluding coordinated increases in transcripts and proteins of citrus\northologs of known plant defense genes. This integrated approach to\nquantifying plant molecular changes in leaves of CLas-infected plants supports the development of diagnostic technology\nfor presymptomatic or early disease detection as part of efforts to\ncontrol the spread of HLB into uninfected citrus groves.