Identification of Genes Expressed Differentially in Grapefruit Infected with Candidatus Liberibacter asiaticus in the Late Stage of Disease

Abstract

Citrus greening or Huanglongbing (HLB), a destructive disease of citrus worldwide, was reported from south of Iran in 2007. The molecular basis of compatibility and disease development in this system is poorly understood. We have carried out a cDNA-AFLP analysis to analyse gene expression of grapefruit infected by Candidatus Leiberibacter asiaticus in the late infection stage. We have applied a cDNA-AFLP approach on grafted infected grapefruit trees at the representing symptoms stage in susceptible host. Selective amplifications with 10 primer combinations allowed the visualization of approximately 24 transcript-derived fragments (TDFs) in the leaves of graft-inoculated trees, which were differentially expressed. We sequenced 14 fragments, which were identified as grapefruit transcripts after homology searching, whereas 12 were not homologous to sequences in NCBI databases. Many grapefruit genes spanning almost all functional categories were upregulated during infection, especially genes involved in ATP synthesize, cytochrome P450 synthesize, isoflavone 2'-hydroxylase, zeaxanthin epoxidase, cellulose synthase, DNA repair protein, aconitate hydratase 2 and citrus tristeza virus resistance gene. This study provides the first global catalogue of grapefruit genes expressed during inoculation, together with their functional annotations. This will help to elucidate the molecular basis of the resistance process and identify genes and chemicals that could help to inhibit the pathogen.