Gustavo Romay

Antiviral defenses in plants through genome editing

Plant–virus interactions based-studies have contributed to increase our understanding on plant resistance mechanisms, providing new tools for crop improvement. In the last two decades, RNA interference, a post-transcriptional gene silencing approach, has been used to induce antiviral defenses in plants with the help of genetic engineering technologies. More recently, the new genome editing systems (GES) are revolutionizing the scope of tools available to confer virus resistance in plants. The most explored GES are zinc finger nucleases, transcription activator-like effector nucleases, and clustered regularly interspaced short palindromic repeats/Cas9 endonuclease. GES are engineered to target and introduce mutations, which can be deleterious, via double-strand breaks at specific DNA sequences by the error-prone non-homologous recombination end-joining pathway. Although GES have been engineered to target DNA, recent discoveries of GES targeting ssRNA molecules, including virus genomes, pave the way for further studies programming plant defense against RNA viruses. Most of plant virus species have an RNA genome and at least 784 species have positive ssRNA. Here, we provide a summary of the latest progress in plant antiviral defenses mediated by GES. In addition, we also discuss briefly the GES perspectives in light of the rebooted debate on genetic modified organisms (GMOs) and the current regulatory frame for agricultural products involving the use of such engineering technologies.

Transmission of tomato Venezuela virus by Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae), in Maracaibo, Venezuela

The biological transmission of Tomato Venezuela virus (ToVEV) by biotype B of the whitefly species Bemisia tabaci (Gennadius) increased (21.7-95.0%), and the time for symptom expression decreased (16-12.6 days) as the number of viruliferous whiteflies allowed access for inoculation to susceptible tomato plants increased from 1 to 20 adults/plant. When acquired only as a nymph, adults of this biotype transmitted the virus to 88.3% of susceptible tomato plants, using 15 viruliferous individuals per test plant, corroborating the circulative nature of the transmission. Disease incidence further increased (up to 100%) when the individuals were allowed to feed again on a virus-infected plant as adults. Leaf area, plant height and dry matter were significantly affected in ToVEV infected tomato plants.

First Report of Bell Pepper Soft-Rot Caused by Pectobacterium carotovorum subsp. brasiliense in Venezuela

Soft rot symptoms were observed during the rainy season, particularly in July, in 2008 on bell pepper (Capsicum annuum L., Hybrid RPP 1216, Syngenta) cultivated under greenhouse conditions (25/18°C, 85% RH) in Sartenejas, Miranda State, Venezuela. Initial symptoms on plants consisted of watery lesions at the basal part of the stem. As the lesions progressed, the whole stem presented water-soaked and necrotic tissue, with detached cortical tissues. Infected plants showed general wilt with defoliation. Fruits showed watery lesions that progressed until complete maceration. Plant samples displaying soft rot symptoms were collected to isolate the causal agent of the disease. Tissue from the lesions was surface-disinfected by standard protocols and ground to prepare serial-dilutions that were plated on Luria Bertani-agar medium. After 48 h of incubation at 28°C, a predominant bacterium was isolated from all samples. Five strains from independent samples were subjected to biochemical and pathogenicity tests. Al...

Complete genome sequence of two tomato-infecting begomoviruses in Venezuela: evidence of a putative novel species and a novel recombinant strain

At least six begomovirus species have been reported infecting tomato in Venezuela. In this study the complete genomes of two tomato-infecting begomovirus isolates (referred to as Trujillo-427 and Zulia-1084) were cloned and sequenced. Both isolates showed the typical genome organization of New World bipartite begomoviruses, with DNA-A genomic components displaying 88.8% and 90.3% similarity with established begomoviruses, for isolates Trujillo-427 and Zulia-1084, respectively. In accordance to the guidelines for begomovirus species demarcation, the Trujillo-427 isolate represents a putative new species and the name “Tomato wrinkled mosaic virus” is proposed. Meanwhile, Zulia-1084 represents a putative new strain classifiable within species Tomato chlorotic leaf distortion virus, for which a recombinant origin is suggested.

Molecular and biological characterization of a new Tomato mild yellow leaf curl Aragua virus strain producing severe symptoms in tomato

Tomato mild yellow leaf curl Aragua virus (ToMYLCV) is a begomovirus first reported infecting tomato (Solanum lycopersicum) and milkweed (Euphorbia heterophylla) in Venezuela. In this study, a ToMYLCV isolate (Zulia-219) was completely sequenced and its host range was evaluated. The DNA-A and DNA-B components of isolate Zulia-219 showed 93 and 85% nucleotide sequence identity with the respective counterparts of the ToMYLCV type strain. According to current demarcation criteria for begomovirus species, Zulia-219 is a new strain of ToMYLCV. Interestingly, tomato plants inoculated with ToMYLCV Zulia-219 displayed severe symptoms, including severe chlorotic leaf curling, in contrast to mild symptoms associated with the type strain of this begomovirus. These results indicate potential risks associated with this new ToMYLCV strain for tomato production in Venezuela.