Evaluating Gene Expression Responses of Citrus to Two Types of Defense Inducers Using a Newly Developed Citrus Agilent Microarray

摘要

Two different types of treatments were applied to evoke defense responses in three citrus cultivars. We used a custom Agilent Citrus microarray (4x44K format) to compare salicylic acid (SA) treated and untreated grapefruit (Citrus paradisi Macf.). Genes previously known to be associated with SA/systemic acquired resistance (pathogenesis-related proteins, lipid metabolic processes, etc.) were observed to be significantly up regulated in treated but not in untreated plants. Genes associated with lignin biosynthesis and auxin metabolism were also up regulated. Down regulated genes included those associated with the jasmonic acid pathway and oxidative stress. A second Agilent microarray experiment was used to compare gene expression responses of two different citrus cultivars to Liberibacter infection. Candidatus Liberibacter asiaticus is a phloem-limited bacterium that is the causal agent of the greening disease, also known as Huanglongbing (HLB). The two cultivars assayed have been reported to have different responses to HLB with sweet orange (Citrus sinensis (L.) Osbeck) being highly susceptible while rough lemon (Citrus jambhiri Lush) is more tolerant to the disease in field observations. The purpose of the experiment was to examine the differences in gene expression between inoculated samples that tested positive for the presence of HLB using polymerase chain reaction (PCR) vs. healthy mock-inoculated plants that tested negative for HLB. Again, genes in the defense pathway were significantly induced in the HLB infected plants. However, different sets of defense-related genes were induced in these two citrus types with distinct responses to HLB.