Molecular insights on potato yellow vein crinivirus infections in the highlands of Colombia.

Potato yellow vein virus (PYVV) was detected in potatoes grown in the Central highlands, north of Bogotá (~3000 m altitude), Colombia. At this altitude viral whitefly vectors are largely absent, but infection persists because of the use of uncertified tubers. Plants with typical PYVV-induced yellowing symptoms, as well as with atypical yellowing or non-symptomatic symptoms were sampled at three separate geographical locations. PYVV presence was assessed by RT-PCR, and several plants were subjected to high-throughput sequencing (HTS) of their small RNA (sRNA) populations. Complete or almost complete sequences of four PYVV isolates were thus reconstructed, all from symptomatic plants. Three viral isolates infected plants singly, while the fourth co-infected the plant together with a potyvirus. Relative proportions of sRNAs to each of the three crinivirus genomic RNAs were found to remain comparable among the four infections. Genomic regions were identified as hotspots of sRNA formation, or as regions that poorly induced sRNAs. Furthermore, PYVV titres in the mixed versus single infections remained comparable, indicating an absence of synergistic/antagonistic effects of the potyvirus on the accumulation of PYVV. Daughter plants raised in the greenhouse from tubers of the infected, field-sampled plants displayed mild PYVV infection symptoms that disappeared with time, demonstrating the occurrence of recovery and asymptomatic infection phenotypes in this pathosystem.

Effects and effectiveness of two RNAi constructs for resistance to Pepper golden mosaic virus in Nicotiana benthamiana plants.

ToChLPV and PepGMV are Begomoviruses that have adapted to a wide host range and are able to cause major diseases in agronomic crops. We analyzed the efficacy of induced resistance to PepGMV in Nicotiana benthamiana plants with two constructs: one construct with homologous sequences derived from PepGMV, and the other construct with heterologous sequences derived from ToChLPV. Plants protected with the heterologous construct showed an efficacy to decrease the severity of symptoms of 45%, while plants protected with the homologous construct showed an efficacy of 80%. Plants protected with the heterologous construct showed a reduction of incidence of 42.86%, while the reduction of incidence in plants protected with the homologous construct was 57.15%. The efficacy to decrease viral load was 95.6% in plants protected with the heterologous construct, and 99.56% in plants protected with the homologous construct. We found, in both constructs, up-regulated key components of the RNAi pathway. This demonstrates that the efficacy of the constructs was due to the activation of the gene silencing mechanism, and is reflected in the decrease of viral genome copies, as well as in recovery phenotype. We present evidence that both constructs are functional and can efficiently induce transient resistance against PepGMV infections. This observation guarantees a further exploration as a strategy to control complex Begomovirus diseases in the field.