Transgenic tobacco plants expressing either a full-length form of the tobacco etch virus (TEV) coat protein or a form truncated at the N terminus of the TEV coat protein were initially susceptible to TEV infection, and typical systemic symptoms developed. However, 3 to 5 weeks after a TEV infection was established, transgenic plants "recovered" from the TEV infection, and new stem and leaf tissue emerged symptom and virus free. A TEV-resistant state was induced in the recovered tissue. The resistance was virus specific. Recovered plant tissue could not be infected with TEV, but was susceptible to the closely related virus, potato virus Y. The resistance phenotype was functional at the single-cell level because protoplasts from recovered transgenic tissue did not support TEV replication. Surprisingly, steady state transgene mRNA levels in recovered tissue were 12-to 22-fold less than transgene mRNA levels in uninoculated transgenic tissue of the same developmental stage. However, nuclear run-off studies suggested that transgene transcription rates in recovered and uninoculated plants were similar. We propose that the resistant state and reduced steady state levels of transgene transcript accumulation are mediated at the cellular level by a cytoplasmic activity that targets specific RNA sequences for inactivation.

A survey was performed in Mexico to study the distribution of Bean common mosaic virus (BCMV) and Bean common mosaic necrosis virus (BCMNV) using a set of primers directed to the coat protein gene (CP) that were designed to detect and characterize the two viral species. Both viral species were present in different locations in the country. BCMV was predominant in the central states of the country, whereas BCMNV proliferated toward the eastern tropical states. The alignment of nine nucleotide sequences for each viral species at the amino region of the CP gene confirmed the identities of the viruses and set the basis to assign them tentatively to pathogroups I, II, and VI.

Translation initiation factor eIF4E exerts an important role during infection of viral species in the family Potyviridae. Particularly, a eIF(iso)4E family member is required for Arabidopsis thaliana susceptibility to Turnip mosaic virus, Lettuce mosaic virus, and Tobacco etch virus (TEV). In addition, a resistance mechanism named restriction of TEV movement (RTM) in A. thaliana controls the systemic spread of TEV in Col-0 ecotype. Here, we describe that TEV-TAMPS, a Mexican isolate, overcomes the RTM resistance mechanism reported for TEV-7DA infection of the Col-0 ecotype but depends on eIF(iso)4E for its systemic spread. To understand at which level eIF(iso)4E participates in A. thaliana TEV-TAMPS infection, the viral RNA replication and translation were measured. The absence or overexpression of eIF(iso)4E did not affect viral translation, and replication was still observed in the absence of eIF(iso)4E. However, the TEV-TAMPS systemic spread was completely abolished in the null mutant. The viral protein genome-linked (VPg) precursor NIa was found in coimmunoprecipitated complexes with both, eIF(iso)4E and eIF4E. However, the viral coat protein (CP) was only present in the eIF(iso)4E complexes. Since both the VPg and the CP proteins are needed for systemic spread, we propose a role of A. thaliana eIF(iso)4E in the movement of TEV-TAMPS within this host.

We report the results of a survey for the presence of Papaya ringspot virus (PRSV) along the coasts of the Gulf of Mexico and the Pacific Ocean, in 15 federal states of Mexico that account for over 98% of the national papaya production. More than 80 locations were visited in 58 counties. Out of a total of 267 papaya leaf samples, 157 tested positive for PRSV. We tested for the presence of three other viruses because of the occurrence of severe, atypical symptoms in plantations. Only Papaya mosaic virus (PapMV) was detected. PRSV was present in every county. PapMV was less frequent, but its overall distribution was almost identical. PRSV and PapMV occurred in single or mixed infections of papaya and other host species that could function as virus reservoirs. We investigated the diversity of the coat protein (CP) sequences of 36 PRSV isolates. The amino acid sequence divergence among all isolates ranged from 0.4 to 9.9%, and was comparable to that found in other regions of the world. In contrast to most of these world regions, there is a clear correlation between CP sequence variation and the geographical origins of the virus isolates.

The study of complex ecological interactions, such as those among host, pathogen, and vector communities, can help to explain host ranges and the emergence of novel pathogens. We evaluated the viromes of papaya orchards, including weed and insect viromes, to identify common viruses in intensive production of papaya in the Pacific Coastal Plain and the Central Depression of Chiapas, Mexico. Samples of papaya cultivar Maradol, susceptible to papaya ringspot virus (PRSV), were categorized by symptoms by local farmers (papaya ringspot symptoms, non-PRSV symptoms, or asymptomatic). These analyses revealed the presence of 61 viruses, where only 4 species were shared among both regions, 16 showed homology to known viruses, and 36 were homologous with genera including Potyvirus, Comovirus, and Tombusvirus (RNA viruses) and Begomovirus and Mastrevirus (DNA viruses). We analyzed the network of associations between viruses and host-location combinations, revealing ecological properties of the network, such as an asymmetric nested pattern, and compared the observed network to null models of network association. Understanding the network structure informs management strategies, for example, revealing the potential role of PRSV in asymptomatic papaya and that weeds may be an important pathogen reservoir. We identify three key management implications: (i) each region may need a customized management strategy; (ii) visual assessment of papaya may be insufficient for PRSV, requiring diagnostic assays; and (iii) weed control within orchards may reduce the risk of virus spread to papaya. Network analysis advances understanding of host-pathogen interactions in the agroecological landscape. IMPORTANCE Virus-virus interactions in plants can modify host symptoms. As a result, disease management strategies may be unsuccessful if they are based solely on visual assessment and diagnostic assays for known individual viruses. Papaya ringspot virus is an important limiting factor for papaya production and likely has interactions with other viruses that are not yet known. Using high-throughput sequencing, we recovered known and novel RNA and DNA viruses from papaya orchards in Chiapas, Mexico, and categorized them by host and, in the case of papaya, symptom type: asymptomatic papaya, papaya with ringspot virus symptoms, papaya with nonringspot symptoms, weeds, and insects. Using network analysis, we demonstrated virus associations within and among host types and described the ecological community patterns. Recovery of viruses from weeds and asymptomatic papaya suggests the need for additional management attention. These analyses contribute to the understanding of the community structure of viruses in the agroecological landscape.