Regulation of gene expression by Candidatus Liberibacter asiaticus in stem and root of Sweet orange (Citrus Sinensis). Citrus sinensis

Candidatus Liberibacter asiaticus infection of citrus is characterized by symptom variability within and among organs. In order to identify molecular processes involved in the regulation of organ response to Ca. Liberibacter infection, the gene expression patterns in C. sinensis leaf, stem, and root was examined in Affymetrix microarray. Our analyses showed that Ca. L. asiaticus reprograms several cellular and metabolic processes in C. sinensis, with most categories regulated in leaves, followed by stems and least in roots. Among them, we identified genes whose expression is regulated in organ-specific manner, reflecting organ specialization in the molecular response to Ca. L. asiaticus. Differences in gene expression were expected between these organs because of functional divergence among them. Overall design: Two-year old Valencia sweet orange (C. sinensis) plants were graft inoculated with budwood from Ca. L. asiaticus-infected citrus plants. Successful infection of the inoculated plants was confirmed in both conventional and quantitative PCR with specific primers to Ca. L. asiaticus. The stem and root samples used for RNA extraction and hybridization on Affymetrix microarrays were obtained from three symptomatic and three healthy control trees of similar size, 16 months after the inoculation.