Implication of the Whitefly, Bemisia tabaci, Collagen Protein in Begomoviruses Acquisition and Transmission

Zinc finger protein 330 regulates Ramie mosaic virus infection in the whitefly Bemisia tabaci MED

BACKGROUND

The whitefly, Bemisia tabaci (Gennadius) is one of the most economically important pests that cause serious damage to agricultural production by transmitting plant pathogenic viruses. Approximately 90% of the virus species transmitted by the whitefly are members of the genus begomovirus. Ramie mosaic virus (RaMoV) is a new bipartite begomovirus that causes severe damage to ramie and several other economic crops in China. In previous studies, we have demonstrated that RaMoV had no obvious direct or indirect effects on B. tabaci. However, whether B. tabaci affects RaMoV infection and the molecular mechanisms of their interaction remain unclear.

RESULTS

Here, we identified a zinc finger protein 330 (ZNF330) in B. tabaci MED interacted with the coat protein (CP) of RaMoV by the yeast two-hybrid assay. Then the interaction between ZNF330 and RaMoV CP was further verified by glutathione S-transferase (GST) pull-down assay. The expression of ZNF330 gene was continuously induced after RaMoV infection. ZNF330 negatively regulated RaMoV replication in the B. tabaci MED. Furthermore, the longevity and fecundity of RaMoV-infected female adults were significantly decreased after silencing of ZNF330.

CONCLUSIONS

Our results indicated that the ZNF330 protein was involved in the negative regulation of RaMoV replication in the B. tabaci MED. High viral accumulation caused by ZNF330 silencing is detrimental to fecundity and longevity of the B. tabaci MED. These findings provided a new insight into identifying the binding partners in whitefly with viral CP and fully understanding the complex interactions between begomoviruses and their whitefly vector. © 2023 Society of Chemical Industry.

Factors Determining Transmission of Persistent Viruses by Bemisia tabaci and Emergence of New Virus-Vector Relationships

Many plant viruses depend on insect vectors for their transmission and dissemination. The whitefly Bemisia tabaci (Hemiptera: Aleyrodidae) is one of the most important virus vectors, transmitting more than four hundred virus species, the majority belonging to begomoviruses (Geminiviridae), with their ssDNA genomes. Begomoviruses are transmitted by B. tabaci in a persistent, circulative manner, during which the virus breaches barriers in the digestive, hemolymph, and salivary systems, and interacts with insect proteins along the transmission pathway. These interactions and the tissue tropism in the vector body determine the efficiency and specificity of the transmission. This review describes the mechanisms involved in circulative begomovirus transmission by B. tabaci, focusing on the most studied virus in this regard, namely the tomato yellow leaf curl virus (TYLCV) and its closely related isolates. Additionally, the review aims at drawing attention to the recent knowhow of unorthodox virus—B. tabaci interactions. The recent knowledge of whitefly-mediated transmission of two recombinant poleroviruses (Luteoviridae), a virus group with an ssRNA genome and known to be strictly transmitted with aphids, is discussed with its broader context in the emergence of new whitefly-driven virus diseases.

Bemisia tabaci Vesicle-Associated Membrane Protein 2 Interacts with Begomoviruses and Plays a Role in Virus Acquisition

Begomoviruses cause substantial losses to agricultural production, especially in tropical and subtropical regions, and are exclusively transmitted by members of the whitefly Bemisia tabaci species complex. However, the molecular mechanisms underlying the transmission of begomoviruses by their whitefly vector are not clear. In this study, we found that B. tabaci vesicle-associated membrane protein 2 (BtVAMP2) interacts with the coat protein (CP) of tomato yellow leaf curl virus (TYLCV), an emergent begomovirus that seriously impacts tomato production globally. After infection with TYLCV, the transcription of BtVAMP2 was increased. When the BtVAMP2 protein was blocked by feeding with a specific BtVAMP2 antibody, the quantity of TYLCV in B. tabaci whole body was significantly reduced. BtVAMP2 was found to be conserved among the B. tabaci species complex and also interacts with the CP of Sri Lankan cassava mosaic virus (SLCMV). When feeding with BtVAMP2 antibody, the acquisition quantity of SLCMV in whitefly whole body was also decreased significantly. Overall, our results demonstrate that BtVAMP2 interacts with the CP of begomoviruses and promotes their acquisition by whitefly.

Insect Transmission of Plant Single-Stranded DNA Viruses

Of the approximately 1,200 plant virus species that have been described to date, nearly one-third are single-stranded DNA (ssDNA) viruses, and all are transmitted by insect vectors. However, most studies of vector transmission of plant viruses have focused on RNA viruses. All known plant ssDNA viruses belong to two economically important families, Geminiviridae and Nanoviridae, and in recent years, there have been increased efforts to understand whether they have evolved similar relationships with their respective insect vectors. This review describes the current understanding of ssDNA virus-vector interactions, including how these viruses cross insect vector cellular barriers, the responses of vectors to virus circulation, the possible existence of viral replication within insect vectors, and the three-way virus-vector-plant interactions. Despite recent breakthroughs in our understanding of these viruses, many aspects of plant ssDNA virus transmission remain elusive. More effort is needed to identify insect proteins that mediate the transmission of plant ssDNA viruses and to understand the complex virus-insect-plant three-way interactions in the field during natural infection.

Proteomic Analyses of Whitefly-Begomovirus Interactions Reveal the Inhibitory Role of Tumorous Imaginal Discs in Viral Retention

In nature, plant viruses are mostly transmitted by hemipteran insects, such as aphids, leafhoppers, and whiteflies. However, the molecular mechanisms underlying the interactions between virus and insect vector are poorly known. Here, we investigate the proteomic interactions between tomato yellow leaf curl virus (TYLCV, genus Begomovirus, family Geminiviridae), a plant virus, and its vector whitefly (Bemisia tabaci) species complex. First, using a yeast two-hybrid system, we identified 15 candidate whitefly proteins interacting with the coat protein of TYLCV. GO and KEGG pathway analysis implicated that these 15 whitefly proteins are of different biological functions/processes mainly including metabolic process, cell motility, signal transduction, and response to stimulus. We then found that the whitefly protein tumorous imaginal discs (Tid), one of the 15 whitefly proteins identified, had a stable interaction with TYLCV CP in vitro, and the DnaJ_C domain of Tid_301−499aa may be the viral binding site. During viral retention, the expression of whitefly protein Tid was observed to increase at the protein level, and feeding whiteflies with dsRNA or antibody against Tid resulted in a higher quantity of TYLCV in the whitefly body, suggesting the role of Tid in antiviral infection. Our data indicate that the induction of Tid following viral acquisition is likely a whitefly immune response to TYLCV infection.

Induction of 2-cyanoethyl-isoxazolin-5-one as an antifeedant against the tobacco cutworm (Spodoptera litura) by jasmonic acid in sweet pea leaf

Although sweet pea (Lathyrus odoratus) beans contain toxic β-aminopropionitrile, the plant itself is readily attacked by insects and is, therefore, protected through the use of pesticides. Consequently, the induction of L. odoratus resistance to insect attack via exogenous treatment is promising for pest control development. Screening of inducible elicitor effects showed that treatment of sweet pea foliage with jasmonic acid (JA) can induce antifeeding-based resistance to tobacco cutworm (Spodoptera litura) larvae. Spectroscopic analysis identified 2-cyanoethyl-isoxazolin-5-one (2-CEIX) as the antifeedant with a half-maximal effective concentration of 33.6 µmol/g fr. wt., i.e., exogenous JA treatment induced antifeeding activity due to the accumulation of 2-CEIX. Moreover, 2-CEIX-induced mortality of S. litura larvae was evaluated by a dipping test and the half-maximal lethal dose was determined to be 5.9 mg/mL. Therefore, 2-CEIX was concluded to be a suitable induced resistance target for elicitors or a lead compound for insecticide development.

Transcriptome Analysis of Gene Expression Profiles of Tomato Yellow Leaf Curl Virus-Infected Whiteflies over Different Viral Acquisition Access Periods

Tomato yellow leaf curl virus (TYLCV), which is transmitted by Bemisia tabaci in a persistent-circulative manner, threatens tomato production worldwide. Little is known about the complicated interaction during this process at the molecular level. In this study, viral AAPs at 0 h, 2 h, 6 h, 12 h and 48 h were investigated using a comparative transcriptome analysis to uncover the transcriptional responses of whiteflies to virus infection. Our results have shown that 755, 587, 1140 and 1347 differentially expressed genes (DEGs) were identified in the comparisons of the data of 0 h vs. 2 h, 0 h vs. 6 h, 0 h vs. 12 h and 0 h vs. 48 h, respectively. KEGG analysis showed that DEGs associated with metabolisms and signal transduction were down-regulated in virus-infected whiteflies. Additionally, 16 up-regulated putative transporter genes and 10 down-regulated genes associated with IL-17 signaling pathway were identified by time-associated gene cluster analysis. These data boost our comprehensions on whitefly-TYLCV interactions associated with different viral AAPs.

Implication of whitefly vesicle associated membrane protein-associated protein B in the transmission of Tomato yellow leaf curl virus

Tomato yellow leaf curl virus (TYLCV) poses serious threat to tomato production worldwide, and the vector, Bemisia tabaci, plays a key role in the transmission of this virus. However, the molecular mechanisms underlying the transmission remain poorly understood. In this study, firstly, we identified the whitefly proteins that presumably interact with TYLCV coat protein (CP) using split-ubiquitin yeast two-hybrid system. Next, we conducted GST pull-down and immunofluorescence to examine the potential interaction between TYLCV CP and one of the proteins identified, namely vesicle associated membrane protein-associated protein B (VAPB), an protein abundantly expressed in whitefly midgut. Further experiments demonstrated that VAPB was significantly up-regulated upon virus acquisition, and silencing VAPB led to a significant increase of relative virus quantity in whitefly haemolymph and salivary glands, as well as an increase of TYLCV transmission efficiency. These findings indicate an important role of VAPB in the transmission of TYLCV by whiteflies.

Plant Antiviral Immunity Against Geminiviruses and Viral Counter-Defense for Survival

The family Geminiviridae includes plant-infecting viruses whose genomes are composed of one or two circular non-enveloped ssDNAs(+) of about 2.5-5.2 kb each in size. These insect-transmissible geminiviruses cause significant crop losses across continents and pose a serious threat to food security. Under the control of promoters generally located within the intergenic region, their genomes encode five to eight ORFs from overlapping viral transcripts. Most proteins encoded by geminiviruses perform multiple functions, such as suppressing defense responses, hijacking ubiquitin-proteasomal pathways, altering hormonal responses, manipulating cell cycle regulation, and exploiting protein-signaling cascades. Geminiviruses establish complex but coordinated interactions with several host elements to spread and facilitate successful infection cycles. Consequently, plants have evolved several multilayered defense strategies against geminivirus infection and distribution. Recent studies on the evasion of host-mediated resistance factors by various geminivirus proteins through novel mechanisms have provided new insights into the development of antiviral strategies against geminiviruses. This review summarizes the current knowledge concerning virus movement within and between cells, as well as the recent advances in our understanding of the biological roles of virus-encoded proteins in manipulating host-mediated responses and insect transmission. This review also highlights unexplored areas that may increase our understanding of the biology of geminiviruses and how to combat these important plant pathogens.