Transcriptome profiling of periwinkle infected with Huanglongbing (‘Candidatus Liberibacter asiaticus’)

Citrus Huanglongbing (HLB) is the most devastating disease of citrus worldwide. It is caused by a phloem-limited α-proteobacterium ‘Candidatus Liberibacter’, whose pathogenesis is unknown. Periwinkle (Catharanthus roseus), known to carry more HLB bacterium and develop HLB symptom in a short period of time, is an ideal host plant for studying the HLB bacterium. In this study, periwinkle was used as the host for HLB bacterium, and the next-generation sequencing technology RNA-Seq was used to evaluate the gene expression of the pairwise comparison for three categories of periwinkle leaf samples, including: healthy leaves (H), yellow leaves (Y), and symptom-just-occurred partially mottled leaves (S). The analysis identified 5432 differentially expressed genes (DEGs), associated with a wide range of functions and pathways involved in cell wall, transport, transcription factors, secondary metabolism, stress, signaling, plant hormone metabolism and signal transduction pathway, starch and sucrose metabolism pathway and photosystem and photosynthesis related pathways. The number of DEGs in the pairwise comparisons between Y and H is much more than that of between S and H. A total of 17 genes were further assayed by real-time qRT-PCR and the results were generally consistent with what obtained from RNA-Seq, with the correlation coefficients all greater than 0.92. The expressions of some genes regulated by the infection of HLB bacterium in periwinkles were consistent with previous studies on citrus. Genes involved in functions such as starch metabolism and hormone mediated defense are considered as useful guidance for HLB pathogenesis in future.