Abstract
BackgroundHuanglongbing (HLB) is arguably the most destructive disease for the citrus industry. HLB is caused by infection of the bacterium, Candidatus Liberibacter spp. Several citrus GeneChip studies have revealed thousands of genes that are up- or down-regulated by infection with Ca. Liberibacter asiaticus. However, whether and how these host genes act to protect against HLB remains poorly understood.ResultsAs a first step towards a mechanistic view of citrus in response to the HLB bacterial infection, we performed a comparative transcriptome analysis and found that a total of 21 Probesets are commonly up-regulated by the HLB bacterial infection. In addition, a number of genes are likely regulated specifically at early, late or very late stages of the infection. Furthermore, using Pearson correlation coefficient-based gene coexpression analysis, we constructed a citrus HLB response network consisting of 3,507 Probesets and 56,287 interactions. Genes involved in carbohydrate and nitrogen metabolic processes, transport, defense, signaling and hormone response were overrepresented in the HLB response network and the subnetworks for these processes were constructed. Analysis of the defense and hormone response subnetworks indicates that hormone response is interconnected with defense response. In addition, mapping the commonly up-regulated HLB responsive genes into the HLB response network resulted in a core subnetwork where transport plays a key role in the citrus response to the HLB bacterial infection. Moreover, analysis of a phloem protein subnetwork indicates a role for this protein and zinc transporters or zinc-binding proteins in the citrus HLB defense response.ConclusionThrough integrating transcriptome comparison and gene coexpression network analysis, we have provided for the first time a systems view of citrus in response to the Ca. Liberibacter spp. infection causing HLB.
Highlights
Huanglongbing (HLB) is arguably the most destructive disease for the citrus industry
HLB is caused by infection of the bacterium, Candidatus Liberibacter spp., which is spread to plants via the vector Asian citrus psyllid (Diaphorina citri) or through grafting of a diseased shoot
Two sets of the citrus Affymetrix GeneChip data derived from very recent publications [11,12] were retrieved from the NCBI Gene Expression Omnibus (GEO) database, while the data for the two earlier reports were provided by Drs Bowman [10] and Wang [5], respectively
Summary
Huanglongbing (HLB) is arguably the most destructive disease for the citrus industry. HLB is caused by infection of the bacterium, Candidatus Liberibacter spp. Several citrus GeneChip studies have revealed thousands of genes that are up- or down-regulated by infection with Ca. Liberibacter asiaticus. Among the major biotic factors which frequently challenge tree growth and fruit development, Huanglongbing (HLB) or called citrus greening is one of the most destructive diseases. HLB was first reported in 1919 in southern China, and very recently it has been reported in almost all major citrus production areas [1,2,3]. HLB is caused by infection of the bacterium, Candidatus Liberibacter spp., which is spread to plants via the vector Asian citrus psyllid (Diaphorina citri) or through grafting of a diseased shoot. Because of the huge impact of HLB in the citrus industry, plant pathologists and horticulturists have long sought after the HLB resistance mechanism in citrus
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