Disrupting insect-mediated transmission of plant viruses

Many plant viruses are vectored by aphids in the non-persistent mode, in which virus particles are transported on these insects’ specialised piercing mouthparts (stylets). Virus infection can change plant-vector interactions and it is thought that this may accelerate virus transmission. To better understand how to inhibit virus transmission, I studied vectoring of cucumber mosaic virus (CMV) and turnip mosaic virus (TuMV) between Arabidopsis thaliana plants by the aphid Myzus persicae. Among other things, I investigated if there were differences in the extent to which the viruses modified aphid-plant interactions in different Arabidopsis accessions, as well as the intrinsic susceptibility of these accessions to aphid infestation. A range of Arabidopsis accessions showed differences in attractiveness and susceptibility to aphids and variations in virus-induced changes in plant-aphid interactions. I found that aphids were attracted to plant volatiles emitted by CMV-infected Col-0 and CMV-infected Ei-2 plants. Interestingly, aphids settle more readily on CMV-infected Ei-2 plants than CMV-infected Col-0 plants. However, aphids did not prefer to settle on CMV-infected plants of either accession. Thus, I used these accessions to determine how to manipulate aphid behaviour to inhibit virus transmission using two types of microcosm: simple lines of plants (with various mixtures of the two accessions) and two-dimensional arrays (‘fields’) of plants. The simple line experiments showed that aphid-mediated transmission could be disrupted using mixtures of accessions with differences in intrinsic aphid attractiveness and susceptibility to aphid infestation. In the two-dimensional ‘field’ experiments, two approaches, which included CMV- and TuMV-resistant plants were most effective in inhibiting virus transmission. Resistant plants in both Arabidopsis backgrounds were either mixed in various proportions (resistant v. susceptible and Col-0 v. Ei-2) in randomised planting layouts or with plants arranged as barriers. A 33% proportion of virus-resistant plants randomly distributed was sufficient to inhibit virus transmission. A barrier of Ei-2 CMV-resistant plants or TuMV-resistant plants in a population of Col-0 plants reduced virus transmission of CMV and TuMV. The latter approach retained more aphids than populations of solely Col-0 plants. Thus, Ei-2 plants can be used as trap plants to attract and ‘sanitise’ viruliferous aphids by inducing them to deposit virus particles in resistant plants, thus inhibiting onward transmission. The results show that there is potential for using intraspecific variation in host plants to inhibit aphid-mediated transmission.Studentship provided by the Ecuadorian Government through SENESCYT (Secretaria de Educación Superior, Ciencia y Tecnología e Innovación

Caracterización morfológica y molecular de accesiones de maíz negro (Zea mays L.) mediante análisis de secuencias simples

Molecular and morphological characterization of maize lines from a breeding program has an important application in the analysis of genetic diversity in order to generate hybrids lines. In the present study, 10 microsatellites (SSR) and 4 morphological traits were used to estimate the genetic relationship among 24 inbred lines of purple maize (Zea mays L.) from Ecuador and CIMMYT. Genetic distance was estimated using the Simple Matching coefficient. As a result, the 24 accessions were grouped in 5 clusters for the morphological traits and in 7 clusters for the molecular analysis using the UPGMA clustering.La caracterización molecular y morfológica de accesiones de maíz dentro de un programa de mejoramiento vegetal es de importante aplicación en la estimación de relaciones genéticas para la generación de híbridos. En este trabajo se emplearon 10 microsatélites y 4 características morfológicas para analizar y estimar el grado de relación genética entre 24 accesiones endocriadas de maíz morado (Zea mays L.) procedentes del Ecuador y del CIMMYT

Bioengineering secreted proteases converts divergent Rcr3 orthologs and paralogs into extracellular immune co-receptors

Secreted immune proteases “Required for Cladosporium resistance-3” (Rcr3) and “Phytophthora-inhibited protease-1” (Pip1) of tomato (Solanum lycopersicum) are both inhibited by Avirulence-2 (Avr2) from the fungal plant pathogen Cladosporium fulvum. However, only Rcr3 acts as a decoy co-receptor that detects Avr2 in the presence of the Cf-2 immune receptor. Here, we identified crucial residues in tomato Rcr3 that are required for Cf-2-mediated signaling and bioengineered various proteases to trigger Avr2/Cf-2-dependent immunity. Despite substantial divergence in Rcr3 orthologs from eggplant (Solanum melongena) and tobacco (Nicotiana spp.), minimal alterations were sufficient to trigger Avr2/Cf-2-mediated immune signaling. By contrast, tomato Pip1 was bioengineered with 16 Rcr3-specific residues to initiate Avr2/Cf-2-triggered immune signaling. These residues cluster on one side of the protein next to the substrate-binding groove, indicating a potential Cf-2 interaction site. Our findings also revealed that Rcr3 and Pip1 have distinct substrate preferences determined by two variant residues and that both are suboptimal for binding Avr2. This study advances our understanding of Avr2 perception and opens avenues to bioengineer proteases to broaden pathogen recognition in other crops