High-throughput transcriptome analysis of the leafy flower transition ofCatharanthus roseusinduced by peanut witches’ broom phytoplasma infection

Abstract

Peanut witches’ broom (PnWB) phytoplasmas are obligate bacteria that cause leafy flower symptoms in Catharanthus roseus. The PnWB-mediated leafy flower transitions were studied to understand the mechanisms underlying the pathogenhost interaction. The whole transcriptome profiles from healthy flowers and stage 4 (S4) PnWB-infected leafy flowers of C. roseus were investigated using next-generation sequencing (NGS). More than 60,000 contigs were generated using a de novo assembly approach, and 34.2% of the contigs (20,711 genes) were annotated as putative genes through name-calling, open reading frame determination, and gene ontology analyses. Furthermore, a customized microarray based on this sequence information was designed and used to further analyze samples at various stages. In the NGS profile, 87.8% of the genes showed expression levels that were consistent with those in the microarray profiles, suggesting that accurate gene expression levels can be detected using NGS. The data revealed that defense-related and flowering gene expression levels were altered in S4 PnWB-infected leafy flowers, indicating that the immunity and reproductive stages of C. roseus were compromised. The network analysis suggested that the expression levels of more than 1,000 candidate genes were highly associated with CrSVP1/2 and CrFT gene expression, which might be crucial in the leafy flower transition. This study provides a new perspective for understanding the mechanisms underlying the leafy flowering transition caused by hostpathogen interactions through analyzing bioinformatics data obtained using a powerful, rapid high-throughput technique.