A single substitution in Vacuolar protein sorting 4 is responsible for resistance to Watermelon mosaic virus in melon

The Molecular Maze of Potyviral and Host Protein Interactions

The negative effects of potyvirus diseases on the agricultural industry are extensive and global. Understanding how protein-protein interactions contribute to potyviral infections is imperative to developing resistant varieties that help counter the threat potyviruses pose. While many protein-protein interactions have been reported, only a fraction are essential for potyviral infection. Accumulating evidence demonstrates that potyviral infection processes are interconnected. For instance, the interaction between the eukaryotic initiation factor 4E (eIF4E) and viral protein genome-linked (VPg) is crucial for both viral translation and protecting viral RNA (vRNA). Additionally, recent evidence for open reading frames on the reverse-sense vRNA and for nonequimolar expression of viral proteins has challenged the previous polyprotein expression model. These discoveries will surely reveal more about the potyviral protein interactome. In this review, we present a synthesis of the potyviral infection cycle and discuss influential past discoveries and recent work on protein-protein interactions in various infection processes.

The alleles bc-ud and bc-ur (previously bc-4 gene), representing coding mutations within Vps4 AAA+ ATPase ESCRT protein, interact with other genes to condition resistance to BCMV and BCMNV in common bean

Bean common mosaic virus (BCMV) and bean common mosaic necrosis virus (BCMNV) have a damaging impact on global common bean (Phaseolus vulgaris L.) cultivation, causing potential yield losses of over 80%. The primary strategy for controlling these viruses is through host plant resistance. This research aimed to identify and validate structural variations for the bc-ud gene as revealed by long-read sequencing, develop an efficient DNA marker to assist selection of bc-ud in snap and dry beans, and examine the interactions between the bc-ud allele and other BCMV resistance genes. A gene (Phvul.005G125100) model on chromosome Pv05, encoding a vacuolar protein-sorting 4 (Vps4) AAA+ ATPase endosomal sorting complexes required for transport (ESCRT) protein, was identified as the best candidate gene for bc-ud. An 84-bp repetitive insertion variant within the gene, exhibited 100% co-segregation with the bc-ud resistance allele across 264 common bean accessions. The 84-bp repetitive insertion was labeled with an indel marker IND_05_36225873 which was useful for tracking the bc-ud allele across diverse germplasm. A different single nucleotide polymorphism variant within the same candidate gene was associated with the bc-4 gene. Segregation in F2 populations confirmed bc-ud and bc-4 were alleles, so bc-4 was renamed bc-ur to fit gene nomenclature guidelines. The interactions of bc-ud and bc-ur with other resistance genes, such as bc-1 (receptor-like kinase on Pv03) and bc-2 (Vps4 AAA+ ATPase ESCRT protein on Pv11), validated gene combinations in the differential "host groups" effective against specific BCMV/BCMNV "pathogroups." These findings increase our understanding of the Bc-u locus, and enhance our ability to develop more resilient bean varieties through marker-assisted selection, reducing the impact of BCMV and BCMNV.

Insights into the early transcriptomic response against watermelon mosaic virus in melon

BACKGROUND

Watermelon mosaic virus (WMV) is one of the most prevalent viruses affecting melon worldwide. Recessive resistance to WMV in melon has previously been reported in the African accession TGR-1551. Moreover, the genomic regions associated to the resistance have also been described. Nevertheless, the transcriptomic response that might infer the resistance to this potyvirus has not been explored.

RESULTS

We have performed a comparative transcriptomic analysis using mock and WMV-inoculated plants of the susceptible cultivar "Bola de oro" (BO) and a resistant RIL (Recombinant inbred line) derived from the initial cross between "TGR-1551" and BO. In total, 616 genes were identified as differentially expressed and the weighted gene co-expression network analysis (WGCNA) detected 19 gene clusters (GCs), of which 7 were differentially expressed for the genotype x treatment interaction term. SNPs with a predicted high impact on the protein function were detected within the coding regions of most of the detected DEGs. Moreover, 3 and 16 DEGs were detected within the QTL regions previously described in chromosomes 11 and 5, respectively. In addition to these two specific genomic regions, we also observde large transcriptomic changes from genes spread across the genome in the resistant plants in response to the virus infection. This early response against WMV implied genes involved in plant-pathogen interaction, plant hormone signal transduction, the MAPK signaling pathway or ubiquitin mediated proteolysis, in detriment to the photosynthetic and basal metabolites pathways. Moreover, the gene MELO3C021395, which coded a mediator of RNA polymerase II transcription subunit 33A (MED33A), has been proposed as the candidate gene located on chromosome 11 conferring resistance to WMV.

CONCLUSIONS

The comparative transcriptomic analysis presented here showed that, even though the resistance to WMV in TGR-1551 has a recessive nature, it triggers an active defense response at a transcriptomic level, which involves broad-spectrum resistance mechanisms. Thus, this study represents a step forward on our understanding of the mechanisms underlaying WMV resistance in melon. In addition, it sheds light into a broader topic on the mechanisms of recessive resistances.

A natural substitution of a conserved amino acid in eIF4E confers resistance against multiple potyviruses

Eukaryotic translation initiation factor 4E (eIF4E), which plays a pivotal role in initiating translation in eukaryotic organisms, is often hijacked by the viral genome-linked protein to facilitate the infection of potyviruses. In this study, we found that the naturally occurring amino acid substitution D71G in eIF4E is widely present in potyvirus-resistant watermelon accessions and disrupts the interaction between watermelon eIF4E and viral genome-linked protein of papaya ringspot virus-watermelon strain, zucchini yellow mosaic virus or watermelon mosaic virus. Multiple sequence alignment and protein modelling showed that the amino acid residue D71 located in the cap-binding pocket of eIF4E is strictly conserved in many plant species. The mutation D71G in watermelon eIF4E conferred resistance against papaya ringspot virus-watermelon strain and zucchini yellow mosaic virus, and the equivalent mutation D55G in tobacco eIF4E conferred resistance to potato virus Y. Therefore, our finding provides a potential precise target for breeding plants resistant to multiple potyviruses.

cmv1-Mediated Resistance to CMV in Melon Can Be Overcome by Mixed Infections with Potyviruses

Resistance to cucumber mosaic virus (CMV) strain LS in melon is controlled by the gene cmv1, which restricts phloem entry. In nature, CMV is commonly found in mixed infections, particularly with potyviruses, where a synergistic effect is frequently produced. We have explored the possibility that this synergism could help CMV-LS to overcome cmv1-mediated resistance. We demonstrate that during mixed infection with a potyvirus, CMV-LS is able to overcome cmv1-controlled resistance and develop a systemic infection and that this ability does not depend on an increased accumulation of CMV-LS in mechanically inoculated cotyledons. Likewise, during a mixed infection initiated by aphids, the natural vector of both cucumoviruses and potyviruses that can very efficiently inoculate plants with a low number of virions, CMV-LS also overcomes cmv1-controlled resistance. This indicates that in the presence of a potyvirus, even a very low amount of inoculum, can be sufficient to surpass the resistance and initiate the infection. These results indicate that there is an important risk for this resistance to be broken in nature as a consequence of mixed infections, and therefore, its deployment in elite cultivars would not be enough to ensure a long-lasting resistance.

Distinct Mechanisms of Endomembrane Reorganization Determine Dissimilar Transport Pathways in Plant RNA Viruses

Plant viruses exploit the endomembrane system of infected cells for their replication and cell-to-cell transport. The replication of viral RNA genomes occurs in the cytoplasm in association with reorganized endomembrane compartments induced by virus-encoded proteins and is coupled with the virus intercellular transport via plasmodesmata that connect neighboring cells in plant tissues. The transport of virus genomes to and through plasmodesmata requires virus-encoded movement proteins (MPs). Distantly related plant viruses encode different MP sets, or virus transport systems, which vary in the number of MPs and their properties, suggesting their functional differences. Here, we discuss two distinct virus transport pathways based on either the modification of the endoplasmic reticulum tubules or the formation of motile vesicles detached from the endoplasmic reticulum and targeted to endosomes. The viruses with the movement proteins encoded by the triple gene block exemplify the first, and the potyviral system is the example of the second type. These transport systems use unrelated mechanisms of endomembrane reorganization. We emphasize that the mode of virus interaction with cell endomembranes determines the mechanism of plant virus cell-to-cell transport.