The Whitefly Bemisia tabaci Knottin-1 Gene Is Implicated in Regulating the Quantity of Tomato Yellow Leaf Curl Virus Ingested and Transmitted by the Insect

Abstract

The whitefly Bemisia tabaci is a major pest to agricultural crops. It transmits begomoviruses, such as Tomato yellow leaf curl virus (TYLCV), in a circular, persistent fashion. Transcriptome analyses revealed that B. tabaci knottin genes were responsive to various stresses. Upon ingestion of tomato begomoviruses, two of the four knottin genes were upregulated, knot-1 (with the highest expression) and knot-3. In this study, we examined the involvement of B. tabaci knottin genes in relation to TYLCV circulative transmission. Knottins were silenced by feeding whiteflies with knottin dsRNA via detached tomato leaves. Large amounts of knot-1 transcripts were present in the abdomen of whiteflies, an obligatory transit site of begomoviruses in their circulative transmission pathway; knot-1 silencing significantly depleted the abdomen from knot-1 transcripts. Knot-1 silencing led to an increase in the amounts of TYLCV ingested by the insects and transmitted to tomato test plants by several orders of magnitude. This effect was not observed following knot-3 silencing. Hence, knot-1 plays a role in restricting the quantity of virions an insect may acquire and transmit. We suggest that knot-1 protects B. tabaci against deleterious effects caused by TYLCV by limiting the amount of virus associated with the whitefly vector.

Enhancing RNAi Efficiency to Decipher the Functional Response of Potential Genes in Bemisia tabaci AsiaII-1 (Gennadius) Through dsRNA Feeding Assays

“…Silencing of k-1 also led to significant increase in virus titer in vector B. tabaci which ultimately increased the percentage transmission by 50% in cotton plants at 14 dpi compared to control. These results are in accordance with previous report which used leaf mediated dip assay to target k-1 gene in whiteflies and found that its downregulation led to increased amount of virus with in the whiteflies and tomato plants (Hariton Shalev et al, 2016). Hence, this study supports the earlier reports, which suggested that Hsp and k-1 modulate virus titer in such a way which limits the virus titer to such a level so that it does not lead to any harmful effect inside whitefly body.…”

“…The target gene sequences were pulled out from whitefly genome database 1 . Selection of genes was done on the basis of their functional role i.e., osmoregulation (Aquaporin (AQP) (Benoit et al, 2014), Calcitonin (CAL) (Furuya et al, 2000;Cohen, 2012;Zandawala, 2012), virus transmission (Cyclophilin B (CYCP) (Kanakala and Ghanim, 2016), Knottin (k-1) (Hariton Shalev et al, 2016), Heat shock proteins i.e., Hsp20, Hsp40 and Hsp70 (Gotz et al, 2012;Gorovits and Czosnek, 2017) and other genes associated with vital processes i.e., SNF7 (SWItch/Sucrose Non-Fermentable) and IAP (inhibitor of apoptosis) (Blitvich et al, 2002). The expression of these genes was validated using gene specific primers (designed using Primer3 software) ( Table 1) in qRT-PCR performed using LightCycler R 96 System (Roche life sciences, Mannheim, German) with SYBR-Green detection (SYBR R Premix Ex TaqTMII, Takara).…”

Downregulation of dystrophin expression in pupae of the whitefly Bemisia tabaci inhibits the emergence of adults

“…Then the vials containing the dsRNA (0.5 μg/μl) and the plantlets were placed in a 1000‐ml glass beaker. Adult whiteflies were released into this silencing system and the beaker was covered with four layers of muslin held with a rubber band (Luan et al , ; Hariton‐Shalev et al ., ). The whiteflies were left to feed and lay eggs on the leaves for the time periods indicated (Fig.…”

“…Then, the insects were collected and allowed to feed on young TYLCV‐infected plants, using clip cages (about 20 insects per cage; six plants for control and six for treatment). After 12 h, the insects were collected, DNA was extracted and the relative amounts of TYLCV were measured by qPCR as described before (Hariton Shalev et al , ).…”

Potential of RNA interference in the study and management of the whitefly, Bemisia tabaci

“…A leaf‐mediated silencing approach was used to investigate the function of knottin genes in the interaction between tomato yellow leaf curl virus (TYLCV) and its whitefly vector (Hariton Shalev et al, ). A family of four knottin‐like genes, named knot‐1 to knot‐4 , was found to be involved in the virus transmission by whiteflies (Leshkowitz et al, ).…”