Vertical and horizontal transmission of plant viruses: two extremes of a continuum?

The four Ws of viruses: Where, Which, What and Why - A deep dive into viral evolution

For centuries, humanity has been captivated by evolution, seeking to unravel the origins of life and identify past patterns with future applications. Viruses, despite their obligate parasitic nature, are the most adaptable biological entities, surpassing cellular life in their variability and adaptability. While many theories about viral evolution exist, a consensus on their origins remains elusive. The quasispecies theory, however, has emerged as a leading framework for understanding viral evolution and, indirectly, their variability and adaptability. This theory illuminates how viruses regulate behaviours such as host range and their symbiotic or antagonistic interactions with hosts. This review delves into the most substantiated theories of viral evolution, addressing four fundamental questions relevant to virus ecology: Where did viruses originate? What factors drive viral evolution? What determines the virus host range? And why do viruses adopt pathogenic or mutualistic strategies? We will provide a comprehensive and up-to-date analysis that integrates diverse theoretical perspectives with empirical data, providing a holistic view of viral evolution and its implications for viral behaviour.

An Integrated Analysis of the Passifloraceae Virome Using Public Domain Data

Passifloraceae is a plant family that includes several species of interest in the food, medicinal, and ornamental industries. The most relevant species are the purple and yellow varieties of Passiflora edulis, which are among the most highly prized tropical fruits in the international markets. Unfortunately, the rapid expansion of this crop worldwide has resulted in the emergence of several viral diseases that endanger the productivity of this crop. In this work, we performed an integrated analysis of the Passifloraceae virome using public data. We investigated PubMed and GenBank records and analyzed all the transcriptome data available for members of this plant family. This analysis resulted in the identification of six novel virus associations and six putative new viral species. We also used RNA sequencing data from public databases to inspect virus accumulation levels and mixed infections. Using network analysis, we also examined the global distribution of Passiflora viruses and their associations with alternative hosts, which is valuable information for implementing viral disease management strategies. Our data suggest that a large diversity of viruses remains to be discovered. Finally, we used the information gathered in this work to estimate the cross-transmission risk of viruses in Colombian Passiflora fields.

Long-Term Effects of Vegetative-Propagation-Mediated TuMV-ZR Transmission on Yield, Quality, and Stress Resistance in Pseudostellaria heterophylla

Pseudostellaria heterophylla (Miq.) Pax (P. heterophylla) was a valued traditional Chinese herbal medicine. Previous studies have shown that P. heterophylla TuMV spreads during the vegetative propagation cycle using tuberous roots as carriers. However, the transmission mechanism of TuMV in P. heterophylla and its effects on host growth remain to be elucidated. In this study, virus-free P. heterophylla culture seedlings were infected with control, TuMV-ZR, and TuMV-ZR-EGFP, thereby resulting in the initial infection cycle of IF1 (TIF1, TEIF1) and control NIF1, and used these roots to propagate the subsequent infection cycle IF2 (TIF2, TEIF2) and control NIF2. The transmission of TuMV-ZR seedlings was tracked by EGFP signal, and their yield, quality, and resistance were analyzed simultaneously in the critical growth period of the plants. The results indicated that TuMV-ZR accumulated in the tuberous roots of IF1 plants, subsequently migrated to IF2 during seedling growth, and was re-stored in IF2 tuberous roots, thereby forming a simple virus transmission cycle. Meanwhile, the tuberous roots of IF1 and IF2 P. heterophylla showed lower fresh weight, dry weight, soluble sugar, and saponin levels compared to NIF1 and NIF2, respectively. TuMV caused a significant reduction in chlorophyll synthesis in IF1 and IF2 P. heterophylla, resulting in impairment to their photosynthetic organs and efficiency. The measurement of stress resistance in IF1 and IF2 P. heterophylla revealed that continuous viral infection disrupted antioxidant enzyme activity, increased the content of MDA, enhanced the activity of PAL, and elevated the levels of intracellular osmotic substances in both propagation cycles. The findings indicated that the accumulation of the TuMV-ZR virus during two successive vegetative propagation cycles induced physiological stress, impaired photosynthesis, and caused progressive yield and quality decline with each cycle. This study systematically examined the impact of TuMV-ZR persistence during vegetative propagation on key physiological and biochemical indices in P. heterophylla, providing critical data to clarify vegetative-propagation-mediated germplasm degradation.

Cucurbit Leaf Crumple Virus Is Seed Transmitted in Yellow Squash (Cucurbita pepo)

The traditional understanding of begomovirus transmission exclusively through the whitefly Bemisia tabaci (Gennadius) has shifted with findings of seed transmission in some begomoviruses over the last decade. We investigated the seed transmissibility of cucurbit leaf crumple virus (CuLCrV), a bipartite begomovirus that has recently emerged as a severe constraint for yellow squash (Cucurbita pepo L.) production in the southeastern United States. We found a high concentration of CuLCrV in the male and female flower tissues of infected squash, including the pollen and ovules. The virus infiltrated the fruit tissues, including the endocarp and funiculus, which are anatomically positioned adjacent to the seeds. In seeds, CuLCrV was detected in the endosperm and embryo, where there are no vascular connections, in addition to the seed coat. The virus was detected in the radicle, plumule, cotyledonary leaves, and true leaves of seedlings grown from seeds collected from infected fruits. In the grow-out test conducted, CuLCrV infections ranged from 17 to 56% of the progeny plants. To ensure that partial viral genome fragments were not being mistaken for replicative forms of the virus, we performed rolling circle amplification PCR and amplified complete DNA-A and DNA-B of CuLCrV from seed tissues, seedlings, and progeny plants of CuLCrV-infected squash. Near-complete DNA-A and DNA-B sequences of CuLCrV were recovered from a progeny plant, further validating our findings. Our results demonstrate that CuLCrV can translocate from vegetative to reproductive tissues of yellow squash, persist within the seeds, and subsequently induce infection in progeny plants, confirming its capacity for seed transmission.

Teratogenic parasites: disease mechanisms and emerging study models

Congenital infections are a leading preventable cause of pregnancy complications impacting both mother and fetus. Although advancements have been made in understanding various congenital infections, the mechanisms of parasitic infections during pregnancy remain poorly understood. This review covers the global incidence of three parasites capable of congenital transmission - Trypanosoma cruzi, Plasmodium spp., and Toxoplasma gondii - and the state of research into their transplacental transmission strategies. We highlight technological advancements in placental modeling that offer opportunities to reveal how parasites cause gestational pathology. Additionally, we discuss the likelihood that selective adaptation contributed to the evolution of mechanisms that facilitate placental infection. These insights provide a foundation for understanding the progression and pathology of congenital parasitic diseases and identifying future research directions.