Role Of Aptamers In Plant Defense Mechanism Against Viral Diseases

Abstract

The diseases of plants caused by viruses are always in main concern for researchers because they reduced the yield and quality of food grains or horticultural products like fruits, vegetables and flowers which will leads a major economic loss of agricultural stakeholders. Presently there is no direct control strategy for viral infection in plants. Advancement in technology leads a novel approach which uses peptide aptamers for controlling plant virus. This technology is effective because the peptide aptamers are specific and binds directly with the capsid protein (CP), nucleoproteins (N) and movement proteins (MP) and affect viral replication machinery of plant virus. In this chapter, we reviewed the about role of peptide aptamers for inhibiting the viral infection in plants.

Introduction

The ever increasing population increases the demands food security at global level for food quality and quantity. But the challenges of climate change leads to the condition of drought in some region while heavy rainfall in other parts of the world and appearance of more new insects or new viruses and new strains. This imbalance the ecological sustainability and cause various type of pathogen infection to the food crops due to fungi, bacteria and viruses. Plant viruses are small pathogens which utilize the host machinery for replication and generation of progeny. The top ten plant viruses are Tobacco mosaic virus (TMV) belongs to genus Tobamovirus cause disease in Tobacco, tomato, and other Solanaceae, Tomato spotted wilt virus (TSWV) belongs to genus Tospovirus cause disease in Over 1000 species in 85 families, including many vegetables, peanuts and tobacco, Tomato yellow leaf curl virus (TYLCV) belongs to genus Begomovirus cause disease in mostly tomato and other Solanaceae and African cassava mosaic virus (ACMV) cause disease in Cassava, Nicotiana and Datura which belongs to genus Begomovirus, Cucumber mosaic virus (CMV) belongs to genus Cucumuvirus cause disease in Cucumbers, squash, melons, peppers, beans, tomatoes, carrots, celery, lettuce, spinach, various weeds and many ornamental plants, Potato virus Y (PVY) cause disease in pepper, potato, tobacco, tomato, some ornamental plants and many weeds and Plum pox virus (PPV) cause disease in Stone fruits including peaches, apricots, plums, nectarines, almonds and sweet and sour cherries belongs to genus Potyvirus, Cauliflower mosaic virus (CaMV) belongs to genus Caulimovirus cause disease in Arabidopsis thaliana, Brassica spp., Raphanus spp. and other species of Brassicaceae and Resedaceae, Brome mosaic virus (BMV) belongs to genus Bromovirus cause disease in Mainly monocots such as barley and others in the grass family and Potato virus X (PVX) belongs to genus Potexvirus cause disease in Potato and other Solanaceae.

The knowledge of pathogen is a determining factor for accurate diagnosis and control of any disease. The need of time is searching and developing the new and eco-sustainable strategies for viral diseases to protect the food crops from the commercial loss of farmers and other stakeholders (Mendoza-Figueroa et al., 2014). Presently there are various strategies for protection and removal of the phyto-pathogens like use of pesticide, RNA interference, Antisense technology, transgenic approaches. While the viral disease are not possible to control by chemicals. Thus, viral diseases are controlled by implementing different strategies like rotation of crop, pathogen-free plant production through tissue culture and though integrated vector management. The traditional breeding technique which take long time and limits of resistance genes is also useful for developing the virus resistant varieties of food crops by exploiting the naturally resistance genes (R genes) in some lines. The resistance genes for viral infection are modified by genetic engineering and used for developing transgenic plants which are resistance against virus.

Alternative methods for plant virus control are use of arbuscular mycorrhizal fungi which improve yield and resistance by providing natural defense in plant (Maffei et al., 2013) and another one is the use of small molecules such as peptides aptamers plays a major role in controlling the viral infection in plants as they are target specific which interfere the replication or gene expressing mechanism of virus. The peptide aptamers are capable to functions in solution as well as under extracellular and intracellular conditions. Thus, it emerged as new potent method of controlling viral diseases efficiency and specificity with wide range of applicability in plant pathology (Mendoza-Figueroa et al., 2014, 2018). In this chapter, we reviewed the about role of peptide aptamers for inhibiting the viral infection in plants

Plant defense Mechanism

The infection of virus in plants is restricted by various mechanism viz. hormone-mediated defence mechanism, protein degradation, regulation of metabolism, gene silencing and immune receptor signalling (Incarbone and Dunoyer, 2013). A two-level detection system which involves plasma membrane-localized and intracellular immune receptors for activating plant defences against invaders involves as innate immunity (Dodds and Rathjen, 2010; Zipfel, 2014). In the first level of defence, PTI is mediated by surface-localized pattern recognition receptors (PRRs), which detect and recognize PAMPs (Bohm et al., 2014; Macho and Zipfel, 2014). The second level, ETI, involves intracellular immune receptors, designated as resistance proteins (R), which recognize – directly or indirectly – virulence effectors secreted by the pathogens into the host intracellular environment (Briddon and Stanley 2009, Shepherd et al., 2009).

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Plant Viral Diseases Controlling Tool: Aptamers

Different strategies for controlling plant virus do not have high levels of resistance due to specificity (Shepherd et al., 2009). The reverse genetics approach by modifying the genome promise the application of Peptide aptamers for broad spectrum resistance against virus in plants. In this approach these aptamers obstruct the function of given gene product after which phenotype is determined (Gong et al., 2014, Rudolph et al., 2003; Lopez-Ochoa et al., 2006) and bioreceptors in bioassays (Yang et al., 2014). There are only few reports on the use of peptide aptamers in this regard which required further confirmation. In general, peptide aptamers appear to act by interfering with protein-protein interactions and blocking the target protein function, such as viral DNA replication, assembly of viral replication complexes and protein complex binding to nucleic acids (Figure-1) (Colombo et al., 2015).

Aptamers attach to molecular targets of proteins, nucleic acids, and even cells, tissues and organisms and can be modified totally in a test tube by chemical synthesis, having sought after storage properties with no immunogenicity in therapeutic applications. Additionally, due to highly complex and refined molecular identified characters, aptamers are competent of attaching tightly and precisely to small molecules with multimeric structures and can inhibit proteins’ biological functions. Aptamers of proteins inside cells are set to interfere with other protein interactions and have a peptide loop joined to a protamerse in scaffolds. Reports on peptides aptamers with antiviral activity are based in the interaction of peptides derivates of common binding microdomain in Nucleoprotein of Tosporvirus as peptides targets, and a library of peptides derivates from other places in N protein of Tospovirus. Results of these study show antiviral activity in Nicotiana benthamiana transgenic plants, peptides that closers interaction, decrease symptoms and viral RNA (Rudolph et al., 2003). Similarly, in another report, transgenic tomato lines expressing peptide aptamers A22 or A64 that bind to Geminivirus replication proteins, exhibited resistant to diverse geminiviruses viz., tomato yellow leaf curl virus or tomato mottle virus (Reyes et al., 2013). Therefore, the peptide aptamer approach can also be expanded to other viral diseases for engineering plants with enhanced resistance.

Scientists developed a method based on aptamers utilizing a highly conserved Replication initiator Protein (ReP/AL1) which required for their replication. In a study using yeast two-hybrid assay discovered that peptides Trx -A22 and A64 were able to strongly bind the Rep/AL1 proteins of nine different viruses (Reyes et al., 2013). These nine Rep/AL1 proteins of the three major genera of the geminivirus family which infect cassava, maize, cotton and vegetables lead major losses. More than 100 geminivirus species cause infection in tomato plants. These were transformed with the Trx-A22 and Trx-A64 peptide aptamers, under the control of the Cauliflower Mosaic Virus (CaMV) E35S constitutive promoter with a duplicated enhancer region. The transgenic lines were infected with either TYLCV or tomato mottle virus (ToMoV) and displayed reduced symptoms and decreased viral DNA loads, further supporting the usage of peptide aptamers as a very promising strategy to enhance crop plant viral resistance (Acero et al., 2011).

A peptide of globulins protein, AmPep1 having antiviral activity which is obtained from amaranth seeds (Amaranthus hypochondriacus). This peptide binds with the origin of replication site (OriRep) of TYLCV and hinders viral replication results in reduction of disease symptoms in Nicotiana benthamiana. It is the direct control of Tomato yellow leaf curl virus (TYLCV) using a peptide from enzymatic digested 11S amaranth globulin without generation of transgenic lines (Mendoza-Figueroa et al., 2018).

Future Scenario

Promising solution of economic losses in food crops is provided by aptamers technology which has broad-spectrum resistance against viral diseases. Conventional breeding approaches combining with the peptide aptamers would be a very powerful strategy to combat new virus species or new variants. RNA inference (RNAi) is homology-dependent and works only with closely related viruses which generate transgenic resistance against plant viruses (Shepherd et al., 2009). The peptide aptamers pairing with RNAi removes the limitations of RNAi while maintaining established resistance to closely related viruses.

The Nucleoproteins and Replication proteins of plant viruses have been used to interfere with peptide aptamers. Now it required to expand for other viral proteins using the peptide aptamer approach and processes to enhance the resistance phenotype in important crops. In future more efficient and specific library should be developed and maintained for aptamers peptide. In addition to the advantages of this technology, also challenges the secondary effects on plant cell which are often observed after expression of complete viral protein. Microbial and fungal infections can also be controlled by peptide aptamer technology (Acero et al., 2011).

Reference

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