Transcriptional Modulation of Plant Defense Genes by a Bipartite Begomovirus Promotes the Performance of Its Whitefly Vector

Abstract

The majority of plant viruses rely on insect vectors for inter-plant transmission. Amid virus transmission, vector-borne viruses such as begomoviruses may significantly modulate host plants in various ways and, in turn, plant palatability to insect vectors. While many case studies on monopartite begomoviruses are available, bipartite begomoviruses are understudied. More importantly, detailed elucidation of the molecular mechanisms involved is limited. Here, we report the mechanisms by which an emerging bipartite begomovirus, the Sri Lankan cassava mosaic virus (SLCMV), modulates plant defenses against whitefly. SLCMV infection of tobacco (Nicotiana tabacum) plants significantly downregulated defenses against whitefly, as whitefly survival and fecundity increased significantly on virus-infected plants when compared to the controls. We then profiled SLCMV-induced transcriptomic changes in plants and identified a repertoire of differentially expressed genes (DEGs). GO enrichment analysis of DEGs demonstrated that the term defense response was significantly enriched. Functional analysis of DEGs associated with defense response revealed that four downregulated DEGs, including putative late blight resistance protein homolog R1B-17 (R1B-17), polygalacturonase inhibitor-like (PGI), serine/threonine protein kinase CDL1-like (CDL1), and Systemin B, directly contributed to plant defenses against whitefly. Taken together, our findings elucidate the role of novel plant factors involved in the modulation of plant defenses against whitefly by a bipartite begomovirus and shed new light on insect vector-virus-host plant tripartite interactions.

Keywords: Bemisia tabaci; Nicotiana tabacum; Sri Lankan cassava mosaic virus; insect vector–virus–plant tripartite interactions; transcriptome.

Figure 1

Effect of SLCMV infection of tobacco plants on plant phenotype and whitefly performance. (A) picture of tobacco plants. Tobacco plants were inoculated with pBINPLUS (empty vector, control) or SLCMV DNA-A+DNA-B. At 25 days post inoculation, plants showing typical symptoms were used for photographing. (B,C) survival and fecundity of Asia II 1 whiteflies on tobacco plants. Ten Asia II 1 whiteflies were released into leaf-clip cages that were placed on tobacco leaves. Whitefly survival and fecundity were recorded seven days post whitefly release. N = 27 for B and C. * p < 0.05 and ** p < 0.01 (independent t-test).

Figure 2

Pearson’s correlation coefficients of overall gene expression patterns between samples. The coefficient values are presented and indicated by the red color.

Figure 3

Volcano plot of differentially expressed genes in SLCMV vs. pBINPLUS. The x-axis represents the log fold change, and the y-axis represents the log significance (p value). Blue dots represent downregulated genes, and red dots represent upregulated genes.

Figure 4

Distribution of the top twenty GO terms in the GO database. The Y-axis represents the name of the GO term, and the X-axis indicates the rich factor. The p value was indicated by the color of the dots, and the number of genes in each term was indicated by the size of the dots.

Figure 5

Effect of SLCMV infection of tobacco plants on the expression of DEGs. (A,B) expression of DEGs. Tobacco plants were inoculated with pBINPLUS (empty vector) and SLCMV DNA-A+DNA-B. Plants were sampled for gene expression analysis at 25 days post inoculation. The number of replicates was 5–6. * p < 0.05 and ** p < 0.01 (independent t-test).

Figure 6

Effects of DEG silencing on whitefly performance. (A,D,G,J,M) Silencing efficiency; (B,E,H,K,N) survival rate of whiteflies on control and virus-induced gene silencing (VIGS) plants; (C,F,I,L,O) fecundity of whiteflies on control and VIGS plants. The number of replicates was 7–19 for (A,D,G,J,M) and 22–31 for (B,C,E,F,H,I,K,L,N,O). * p < 0.05, ** p < 0.01, and *** p < 0.001 (independent t-test).