Ritesh Mishra

Systemic Infection of Potyvirus: A Compatible Interaction Between Host and Viral Proteins

Viruses profoundly depend on endogenous host transport system and interact with preexisting host cellular factors during movement. Potyviral movement is directed by several movement proteins that are HC-Pro, CP, VPg, and CI and newly discovered P3N-PIPO. CP and HC-Pro facilitate movement of virus by increasing size exclusion limit (SEL) of plasmodesmata (PD). These movement proteins serve many functions: binding the viral genome, transporting the viral genome to plasmodesmata, gating plasmodesmata, trafficking through plasmodesmata, and then transporting through phloem. TuMV P3N-PIPO is a PD-localized protein and mediates the targeting of CI to PD. The P3 protein was not previously associated with potyvirus movement, but it was known to interact with the P1 protein; it is co-localized with 6K2 vesicles (site of potyviral replication). This points out a link between virus replication complexes and intracellular movement. CP has the ability to increase SEL of PD and interact with host RTM factors and suppress RTM resistance of plants. HC-Pro is crucial for long-distance movement of potyvirus by suppressing gene silencing mechanism of host plant. Interaction with host factors and chaperones is also required for efficient spread of potyvirus; presumably interaction of the viral CP with a plant Dna J-like protein NtCPIP (capsid protein interacting proteins) provides a strong in vivo confirmation for the essential role of plant chaperones in potyvirus movement. In this chapter, we are concerned on potyvirus intracellular, intercellular, and long-distance movement, focusing on the host cellular factors’ interaction with movement proteins involved.

Current status of Potyvirus in India

Potyvirus particles are flexuous rods of 700–900 nm in length and contain one positive sense single-stranded genomic RNA molecule of approximately 10 kb, which is encapsidated by a single type of coat protein. According to available NCBI database, Potyvirus infection is prominently present in Solanaceae, Leguminosae and Cucurbitaceae families in India. Potyviruses can induce a wide range of different symptoms in infected host plants including mosaic, stripe, mottling, vein clearing, vein banding, ringspots, necrotic or chlorotic lesions, flower breaking, stunting, wilting, and most commonly lead tostunting and yield losses. PCR-based methods for the detection and identification of potyviruses rely on degenerate primers designed for conserved regions. Potyvirus infection requires the interaction of host factors with viral proteins and RNA for its replication and systemic spread, i.e interaction between VPg and eIF4E is required for Potyvirus genome translation. Mutations in host translational initiation factor eIF4E cause the conformational shift in encoded proteins which are unable to bind with viral protein (VPg), resulting in broad-spectrum Potyvirus resistance.

GENETIC VARIABILITY OF THE REPLICASE (NIB) GENE OF PAPAYA RINGSPOT VIRUS IN NORTHERN INDIA INDICATES COMMON ANCESTRY WITH ISOLATES FROM CHINA AND TAIWAN

The purpose of the present study was to investigate the genetic variability and phylogeny of papaya ringspot virus (PRSV) on the basis of NIb (replicase) gene. The NIb and coat protein (CP) regions of about 2.5 kb of seven PRSV isolates from North India were cloned and sequenced. The North Indian isolates R2R and R5R have higher and lower sequence similarity with other PRSV isolates, respectively. Sequence comparison of NIb gene of 42 PRSV isolates, revealed that the average evolutionary divergence of all sequence pairs were 10.6% and 11.2% at amino acid and nucleotide level, respectively. Transitions were more frequent than transversions in the analyzed sequences. Maximum likelihood phylogenetic tree of combined NIb and CP regions indicated the common ancestry of North Indian isolates with Chinese and Taiwanese isolates. One potential recombination breakpoint in isolate R5R, together with its higher sequence identity and common ancestry with Chinese PRSV isolates, suggest the possible import of the former from the Chinese subcontinent.

Interaction between viral proteins with the transmission of Potyvirus

Potyviridae is the largest family in plant viruses, in which a group of potyviruses constitutes a very important role in causing diseases in plants. The organisation of the viral genome is positive-sense RNA, ranging in size from 9000 to 12000 bp. The viral genome encodes a large polyprotein that is processed by three virus-encoded proteinases (two proteinases and helper component proteinase) to yield the mature products. This review concentrates on the interaction between viral proteins with the transmission of Potyvirus. Transmission and long-distance movement of Potyvirus is only possible through vector and that time interaction between two viral proteins takes place, named as helper component-proteinase and coat protein. Interaction between NIb, NIa, 6K2 as well as with CI (helicase activity) also involved in the replication of potyviruses. Some researchers developed a yeast two-hybrid system and biomolecular fluorescence complementation system technology which proved the interaction among the viral protein. At last all proteins are correlated with each other and play a very significant role in the transmission of Potyvirus.