Genomics and Transcriptomics of Candidatus Phytoplasma Asteris Induced Sesame Phyllody Modulating Hormonal and Defense Alterations.

Abstract

Sesame phyllody, a destructive disease caused by phytoplasma infection, induces severe morphological abnormalities, including floral virescence, phyllody, witches' broom, leaf deformation, and stunted growth. This study aimed to characterize phytoplasma isolates from diverse regions of India, identifying them as Candidatus Phytoplasma asteris (16Sr-I), Candidatus Phytoplasma citri (16Sr-II), and Candidatus Phytoplasma australasia (16Sr-II). Whole-genome sequencing of Candidatus Phytoplasma asteris isolate SPGN revealed a genome size of 563,754 bp, encoding 542 proteins, including several genes associated with antibiotic resistance. Effector prediction analysis identified key virulence-associated proteins, such as SAP50-like, SAP34-like, TENGU-su inducer, and immunodominant membrane proteins, which manipulate host development and immune responses. Transcriptomic analysis of infected sesame plants revealed significant gene expression alterations, with upregulated genes linked to floral malformation, vascular tissue modifications, and stress responses, while the downregulated genes were associated with flavonoid metabolism and immune signaling. Phytoplasma infection disrupted hormonal pathways, leading to increased expression of auxin, cytokinin, and gibberellin-related genes, suggesting hormonal dysregulation as a key factor in symptom development. Furthermore, immune suppression was evident through the downregulation of key defense-related genes, including those involved in MAPK signaling and pathogenesis-related protein families. These findings enhance our understanding of phytoplasma pathogenesis in sesame and provide potential targets for developing effective disease management strategies.