Coat proteins of Rice tungro bacilliform virus and Mungbean yellow mosaic virus contain multiple nuclear-localization signals and interact with importin α

Abstract

Transport of the viral genome into the nucleus is an obligatory step in the replication cycle of plant pararetro-and geminiviruses. In both these virus types, the multifunctional coat protein (CP) is thought to be involved in this process. Here, a green fluorescent protein tagging approach was used to demonstrate nuclear import of the CPs of Rice tungro bacilliform virus (RTBV) and Mungbean yellow mosaic virus -Vigna (MYMV) in Nicotiana plumbaginifolia protoplasts. In both cases, at least two nuclear localization signals (NLSs) were identified and characterized. The NLSs of RTBV CP are located within both N-and C-terminal regions (residues 479KRPK/ 497KRK and 744KRK/758RRK), and those of MYMV CP within the N-terminal part (residues 3KR and 41KRRR). The MYMV and RTBV CP NLSs resemble classic mono-and bipartite NLSs, respectively. However, the N-terminal MYMV CP NLS and both RTBV CP NLSs show peculiarities in the number and position of basic residues. In vitro pull-down assays revealed interaction of RTBV and MYMV CPs with the nuclear import factor importin a, suggesting that both CPs are imported into the nucleus via an importin a-dependent pathway. The possibility that this pathway could serve for docking of virions to the nucleus is discussed.

Assessing Global Transcriptome Changes in Response to South African Cassava Mosaic Virus [ZA-99] Infection in Susceptible Arabidopsis thaliana

“…Another interesting gene, 4CL1, is responsible for channelling carbon flow in the phenylpropanoid metabolic pathway. It appears to be involved in cell wall modification as silencing of this gene caused increased cellulose and decreased lignin in general [83], [84]. 4CL1 was shown to be up-regulated at 14 dpi (1.21) and 24 dpi (1.40), and significantly down-regulated at 36 dpi (−2.50) by SACMV, indicating a possible synergistic role, along with ß-1,3-glucanase, in SACMV cell-to-cell movement via cell wall modifications.…”

Coat protein deletion mutation of Mungbean yellow mosaic India virus (MYMIV)

“…However in non permissive species, CP is required (Wang et al 1999). CP is required even in intra cellular movement for facilitating docking of viral genome onto nuclear pore by interacting with α-importin protein as shown for MYMV (Guerra-Peraza et al 2005). Our results indicate that CP is absolutely essential to systemically spread and produce symptoms in cowpea and mungbean.…”

Identification of Host Genes Involved in Geminivirus Infection Using a Reverse Genetics Approach

“…Importin α is a component of the nuclear pore-targeting complex (PTAC) that acts as an adaptor by recognizing the nuclear localization signal (NLS) sequences and binding to importin β. Importin β is the carrier component of PTAC, and targets the complex to the nuclear pore by binding to nuclear pore proteins [69], [70]. Importin α has been shown to interact with the CP from the geminivirus MYMV [71], and this interaction might serve for docking of viruses to the nucleus and facilitating nuclear localization of the CP during encapsidation. In this context, the finding that silencing of IMPA-4 favours the viral infection seems counterintuitive; however, the fact that this gene is overexpressed in response to several pathogens and elicitors ( Arabidopsis eFP browser) suggests that this host factor might also play a role in plant defence, providing a possible explanation for the observed phenotype.…”