Insights on Carica papaya L. proteomic, ultrastructural and physiological changes associated with pre-flowering-related tolerance to papaya sticky disease

The development of Papaya Sticky Disease (PSD), caused by the papaya meleira virus (PMeV) complex, only occurs after flowering, suggesting the presence of tolerance mechanisms during the transition from juvenile to adult papaya plants ( C. papaya ). In this study, 1,609 leaf proteins of C. papaya were quantified using a label-free strategy. Differentially accumulated proteins—38, 130, 160, and 17 at 3, 4, 7, and 9 months post-germination, respectively—indicated modulation of biological processes at each development phase, mainly involving photosynthesis and cell wall remodeling. Juvenile C. papaya plants infected with the PMeV complex showed an accumulation of photosynthetic proteins. Correspondingly, chlorophyll fluorescence results suggested enhanced efficiency in photosystem (PS) II and PSI energy flux in these plants. In parallel, pre-flowering plants exhibited a reduction in cell wall-degrading enzymes, followed by an accumulation of proteins involved in the synthesis of wall precursors post-flowering. These findings, combined with ultrastructural data on laticifers, suggest that C. papaya struggles to maintain the integrity of laticifer walls, ultimately failing to do so after the juvenile-adult transition and resulting in latex exudation, thereby supporting initiatives for the genetic improvement of C. papaya to enhance resistance against the PMeV complex.