Multifunctional roles of geminivirus encoded replication initiator protein

Abstract

Geminivirus infection has been a threat to cultivation worldwide by causing huge losses to the crop. The single-stranded DNA genome of a geminivirus possesses a limited coding potential and many of the open reading frames (ORFs) are overlapping. Out of 5-7 ORFs that a geminivirus genome codes for, the AC1 ORF encodes for the replication initiator protein (Rep) which is involved in the replication of virus within the infected plant cell. Rep is the only viral protein absolutely required for the in planta viral replication. Across different genera of the Geminiviridae family, the AC1 ORF exhibits a high degree of sequence conservation thus it has been used as an effective target for developing broad spectrum resistance against the invading geminiviruses. This multifunctional protein is required for initiation, elongation as well as termination of the viral replication process. Rep is also involved in stimulation of viral transcription. In addition, it also functions as suppressor of gene silencing and is involved in the process of transcription by regulating the expression of certain viral genes. Rep protein also interacts with few viral proteins such as coat protein, replication enhancer protein and with several host factors involved in different pathways and processes for its replication and efficient infection. This review will summarise our current understanding about the role of this early viral protein in viral propagation as well as in establishment of pathogenesis in a permissive host.

A Lysine Residue Essential for Geminivirus Replication Also Controls Nuclear Localization of the Tomato Yellow Leaf Curl Virus Rep Protein

“…Among the few proteins encoded by the geminiviral genome, only one is known to be essential for viral replication, namely, the replication initiator protein (Rep), also called AL1, AC1, or C1. Rep is the most conserved geminiviral protein and exerts a plethora of functions inside the host nucleus (35), such as virus-specific recognition of its cognate origin of replication (36,37), transcriptional repression of the viral genes (38), binding of dsDNA (39,40), DNA nicking, and DNA helicase activity on viral DNA (41)(42)(43)(44). Moreover, Rep interacts with many proteins.…”

Identification of Tomato Proteins That Interact With Replication Initiator Protein (Rep) of the Geminivirus TYLCV

“…In total 30% of the identified proteins was assigned to be nucleus based on their annotation ( Figure 2D ). In order to visualize the Rep-interactome, we plotted the 54 tomato proteins in a protein interaction network ( Figure 2E ) with the nodes representing (i) the newly identified host proteins (green and yellow), (ii) 16 Rep-interactors derived from previous studies (pink) (reviewed by Ruhel and Chakraborty, 2019 ) and (iii) Rep (blue). In total, seventy known interactions with Rep ( Ruhel and Chakraborty, 2019 ) were included in this protein network (blue edges and dotted edges) and a total of 148 plant protein interactions (grey edges) were retrieved from the STRING database ( Table S3 ).…”

“…A manually curated protein–protein interaction network was constructed with Cytoscape ( Shannon et al., 2003 ). For that, the interaction network of every putative host interactor and the known Rep-interactors, as reported by Ruhel and Chakraborty (2019) were retrieved from the STRING protein database ( ). The resulting nodes (proteins) and edges (interactions) were arranged according to the force-directed layout.…”

“…representing (i) the newly identified host proteins (green and yellow), (ii) 16 Rep-interactors derived from previous studies (pink) (reviewed by Ruhel and Chakraborty, 2019) and (iii) Rep (blue). In total, seventy known interactions with Rep (Ruhel and Chakraborty, 2019) were included in this protein network (blue edges and dotted edges) and a total of 148 plant protein interactions (grey edges) were retrieved from the STRING database (Table S3). This network contained two major clusters.…”

“…Only one viral protein, the Replication initiator protein (Rep), is strictly required for viral replication to occur. In fact, Rep is the most conserved geminiviral protein and it is critical for assembly of viral replisomes, a complex of viral and host proteins that forms a DNA replication fork at viral DNA (Rizvi et al, 2015;Ruhel and Chakraborty, 2019). Numerous studies have been attempted to characterize the composition and mode-of-action of this viral replisome.…”