Juvenile-related tolerance to papaya sticky disease (PSD): proteomic, ultrastructural, and physiological events

The proteomic analysis of PMeV-complex-infected C. papaya unveiled proteins undergoing modulation during the plant's development. The infection notably impacted processes related to photosynthesis and cell wall dynamics. The development of Papaya Sticky Disease (PSD), caused by the papaya meleira virus complex (PMeV-complex), occurs only after the juvenile/adult transition of Carica papaya plants, indicating the presence of tolerance mechanisms during the juvenile development phase. In this study, we quantified 1609 leaf proteins of C. papaya using a label-free strategy. A total of 345 differentially accumulated proteins were identified-38 at 3 months (juvenile), 130 at 4 months (juvenile/adult transition), 160 at 7 months (fruit development), and 17 at 9 months (fruit harvesting)-indicating modulation of biological processes at each developmental phase, primarily related to photosynthesis and cell wall remodeling. Infected 3- and 4-mpg C. papaya exhibited an accumulation of photosynthetic proteins, and chlorophyll fluorescence results suggested enhanced energy flux efficiency in photosystems II and I in these plants. Additionally, 3 and 4-mpg plants showed a reduction in cell wall-degrading enzymes, followed by an accumulation of proteins involved in the synthesis of wall precursors during the 7 and 9-mpg phases. These findings, along with ultrastructural data on laticifers, indicate that C. papaya struggles to maintain the integrity of laticifer walls, ultimately failing to do so after the 4-mpg phase, leading to latex exudation. This supports initiatives for the genetic improvement of C. papaya to enhance resistance against the PMeV-complex.