Proteomic analysis of papaya (Carica papaya L.) displaying typical sticky disease symptoms

Abstract

Papaya (Carica papaya L.) hosts the only described laticifer-infecting virus (Papaya meleira virus, PMeV), which is the causal agent of papaya sticky disease. To understand the systemic effects of PMeV in papaya, we conducted a comprehensive proteomic analysis of leaf samples from healthy and diseased plants grown under field conditions. First, a reference 2-DE map was established for proteins from healthy samples. A total of 486 reproducible spots were identified, and MALDI-TOF-MS/MS data identified 275 proteins accounting for 159 distinct proteins from 231 spots that were annotated. Second, the differential expression of proteins from healthy and diseased leaves was determined through parallel experiments, using 2-DE and DIGE followed by MALDI-TOF-MS/MS and LC-IonTrap-MS/MS, respectively. Conventional 2-DE analysis revealed 75 differentially expressed proteins. Of those, 48 proteins were identified, with 26 being upregulated (U) and 22 downregulated (D). In general, metabolism-related proteins were downregulated, and stress-responsive proteins were upregulated. This expression pattern was corroborated by the results of the DIGE analysis, which identified 79 differentially expressed proteins, with 23 identified (17 U and 6 D). Calreticulin and the proteasome subunits 20S and RPT5a were shown to be upregulated during infection by both 2-DE and DIGE analyses. These data may help shed light on plant responses against stresses and viral infections.

Label-free quantitative proteomic analysis of pre-flowering PMeV-infected Carica papaya L.

“…Opposite to what was previously observed for adult and sticky-diseased C. papaya plants [22], pre-flowering PMeV-infected C. papaya leaves showed lower levels of 26S proteasome-related proteins. In plants, the 26S proteasome system is essential to regulate proteolysis and control the abundance of crucial cellular regulators in response to distinct environmental and developmental cues, including virus infection [47,48].…”

“…endochitinase and PR-4 [22], while latex samples show lower abundance of chymopapain cysteine proteases and a latex serine proteinase inhibitor [6]. Together, this data indicates the existence of systemic acquired resistance (SAR) response in PSD symptomatic plants.…”

“…The GO-based grouping of the identified proteins showed they were largely associated with metabolism, stress responses and cellular organization. C. papaya proteins known to be differentially accumulated in sticky-diseased papaya leaf [22] and latex [6] samples, for instance tubulin beta, HSP70 and latex serine protease inhibitor, were among the identified proteins, suggesting the obtained dataset likely includes other proteins relevant to the pathosystem.…”

“…To our knowledge, previously published studies have used gel (1-and 2-DE and DIGE)-based separations of C. papaya proteins followed by peptide mass spectrometry analysis. In summary, the total number of identified proteins per sample type is 76 from somatic embryos [31], 54 from papaya fruit pulp [32,33], 71 from leaves [22], 186 from latex [6,34] and 1,581 proteins from isolated chromoplasts [35]. In this study, field-grown pre-flowering C. papaya plants' leaf samples were submitted to protein extraction and in-solution digestion, and the resulting peptides were analyzed using an LC-MS/MS based approach.…”

“…Some proteins in this group are already known to be involved with C. papaya x PMeV interaction such as 26s proteasome regulatory subunit, calreticulin and acidic endochitinase (Supplemental Table S3) [6,22]. The group represents a main source of other proteins potentially involved with plant responses to viruses.…”