Comparative proteomic analysis provides new insight into differential transmission of two begomoviruses by a whitefly

Abstract

Background: Viruses in the genus Begomovirus (Family Geminiviridae) include many important economic plant viruses transmitted by whiteflies of the Bemisia tabaci species complex. In general, different begomoviruses may be acquired and transmitted by the same whitefly species with different efficiencies. For example, the species Mediterranean (MED) in this whitefly species complex transmits tomato yellow leaf curl virus (TYLCV) at a higher efficiency than papaya leaf curl China virus (PaLCuCNV). However, the proteomic responses of whitefly to the infection of different begomoviruses remain largely unknown.

Methods: We used iTRAQ-based proteomics coupled with RT-qPCR to investigate and compare responses of the MED whitefly to the infection of TYLCV and PaLCuCNV.

Results: Totally, 259, 395 and 74 differently expressed proteins (DEPs) were identified in the comparisons of TYLCV-infected vs. un-infected, PaLCuCNV-infected vs. un-infected, and TYLCV-infected vs. PaLCuCNV-infected whiteflies, respectively. These proteins appear associated with catabolic process, metabolic process, transport, defense response, cell cycle, and receptor. The comparisons of TYLCV-infected vs. un-infected and PaLCuCNV-infected vs. un-infected shared some similar DEPs, indicating possible involvement of laminin subunit alpha, dystroglycan, integrin alpha-PS2 and cuticle proteins in viral transport as well as the role of putative defense proteins 3 and PITH in anti-viral response. However, 20S proteasome subunits associated with regulation of virus degradation and accumulation were up-regulated in PaLCuCNV-infected but not in TYLCV-infected whiteflies, which may be related to the constraints of PaLCuCNV accumulation in MED.

Conclusions: These findings provide valuable clues for unravelling the roles of some whitefly proteins in begomovirus transmission.

Keywords: Begomovirus; Virus transmission; Whitefly; iTRAQ-based proteomics.

Fig. 1

Workflow illustration. (a) Workflow for obtaining whiteflies used in the treatments. Two cultivars of tomato were used in this study, i.e. S. lycopersicum cv. Hezuo 903 (susceptible) and cv. Zheza 502 (resistant). For each of the three treatments, two biological replicates were conducted. All arrows indicate whitefly transfer. (b) Workflow for iTRAQ analysis.

Fig. 2

Protein expression patterns of MED whiteflies in response to viral infections. Protein expression patterns in whiteflies of TYLCV-infected vs. un-infected (a, b), PaLCuCNV-infected vs. un-infected (c, d), and TYLCV-infected vs. PaLCuCNV-infected (e, f). The Volcano figures of DEPs (a, c and e) depict volcano plot of log₂ fold-change (x-axis) versus -log₁₀ Q value (y-axis, representing the probability that the protein is differentially expressed) in each of the three combination for comparison. P < 0.05 and fold change > 1.2 were set as the significant threshold for differential expression. In each of the three diagrams of (a, c, and e), the red dots indicate significantly up-regulations, and the green dots indicate significant down-regulations, while the black dots indicate no significant changes in regulations

Fig. 3

Gene ontology analysis. The bar chart shows the distribution of corresponding GO terms (P < 0.05). Different colors represent different GO categories. a TYLCV-infected vs. un-infected. b PaLCuCNV-infected vs. un-infected. c TYLCV-infected vs. PaLCuCNV-infected

Fig. 4

Pathway enrichment analysis. Rich factor is the ratio of differentially expressed protein number annotated in this pathway term to all protein number annotated. Greater rich factor means greater intensiveness. P value ranges from 0~1, and lower P value means greater intensiveness. Displayed here are enriched pathway terms with P < 0.05. a TYLCV-infected vs. un-infected, b PaLCuCNV-infected vs. un-infected, and c TYLCV-infected vs. PaLCuCNV-infected

Fig. 5

Hierarchical cluster analysis of DEPs. Fold changes of protein abundance in three combinations of comparison were analyzed using the software Genesis (version 1.8.1)

Fig. 6

qPCR analysis of candidate genes. Values of control group (un-infected whitefly) were all set to 1.0 unit. Error bars represent the standard deviation. Significance is indicated with different letters; Student’s t-test