Investigating Genomic Variability and Molecular Mechanisms of Pathogenesis in ‘Candidatus Phytoplasma solani’

‘Candidatus Phytoplasma solani’ (CaPsol) is a phloem-limited bacterium associated in Europe and the Mediterranean basin with bois noir (BN) disease of grapevine and with stolbur diseases of tomatoes, potatoes and other solanaceous crops. Its ecology is highly intricate, involving various insect vectors, primarily the planthopper Hyalesthes obsoletus, and a diverse range of host plants within agroecosystems. Developing effective control measures requires understanding the complex interactions between the phytoplasma and its hosts. CaPsol pathogenicity relies on effector proteins that disrupt plant hormone signaling, cell cycle regulation, and immune defenses, facilitating colonization, spread, and symptom development. The main aim of this work is to (i) type CaPsol strains from BN-affected grapevines by multiple gene (tufB, stamp, vmp1) sequence analyses and to investigate differences in their virulence studying their prevalence in grapevines exhibiting a range of symptom severity; and (ii) identify genes encoding for phytoplasma secreted effectors from the genomes of nine genetically distinct CaPsol strains to evaluate their expression variations in grapevine. CaPsol genome analysis was performed to identify protein-coding sequences (CDS) using PRODIGAL. Putative effector prediction was done using SignalP and TargetP, focusing on cleavage sites and signal peptides via neural networks and Markov models. InterProScan classified proteins into families and identified functional domains. Molecular typing results showed a high variability and diversity of CaPsol strains infecting grapevines showing severe and mild symptoms. Genome analysis identified 30 effectors, categorized by localization within or outside sequence variable mosaic (SVM) regions. Primers for qPCR were designed to evaluate effector gene expression in grapevine. Findings would improve our understanding of CaPsol-plant interactions, aiding sustainable control strategies.