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Satellites associated with plant or animal viruses have been largely detected and characterized, while those from mycoviruses together with their roles remain far less determined. Three dsRNA segments (dsRNA 1 to 3 termed according to their decreasing sizes) were identified in a strain of phytopathogenic fungus Pestalotiopsis fici AH1-1 isolated from a tea leaf. The complete sequences of dsRNAs 1 to 3, with the sizes of 10316, 5511, and 631 bp, were determined by random cloning together with a RACE protocol. Sequence analyses support that dsRNA1 is a genome of a novel hypovirus belonging to a newly proposed genus “Alphahypovirus” of the family Hypoviridae, tentatively named Pestalotiopsis fici hypovirus 1 (PfHV1); dsRNA2 is a defective RNA (D-RNA) generating from dsRNA1 with septal deletions; and dsRNA3 is the satellite component of PfHV1 since it could be co-precipitated with other dsRNA components in the same sucrose fraction by ultra-centrifuge, suggesting that it is encapsulated together with PfHV1 genomic dsRNAs. Moreover, dsRNA3 shares an identical stretch (170 bp) with dsRNAs 1 and 2 at their 5′ termini and the remaining is heterogenous, which is distinct from a typical satellite that generally has very little or no sequence similarity with helper viruses. More importantly, dsRNA3 lacks a substantial open reading frame (ORF) and a poly (A) tail, which is unlike the known satellite dsRNAs of hypoviruses, as well as unlike those in association with Totiviridae and Partitiviridae since the latters are encapsidated in coat proteins. As up-regulated expression of dsRNA3, dsRNA1 was significantly down-regulated, suggesting that dsRNA3 negatively regulates the expression of dsRNA1, whereas dsRNAs 1 to 3 have no obvious impact on the biological traits of the host fungus including morphologies and virulence. This study indicates that PfHV1 dsRNA3 is a special type of satellite-like nucleic acid that has substantial sequence homology with the host viral genome without encapsidation in a coat protein, which broadens the definition of satellite.IMPORTANCESatellites in association with plant or animal viruses have been largely detected and characterized, while those from mycoviruses together with their roles remain far less determined. Here, a special satellite-like dsRNA (SatL-dsRNA) together with its helper virus, a novel hypovirus from Pestalotiopsis fici, was identified and characterized. This SatL-dsRNA lacks a substantial open reading frame and a poly (A) tail, which is unlike the known satellite dsRNAs of hypoviruses. It is also unlike those in association with Totiviridae and Partitiviridae since the latters are encapsidated in coat proteins. As up-regulated expression of the SatL-dsRNA, the helper virus genome was significantly down-regulated, suggesting that it negatively regulates the genomic expression of the helper virus. This special SatL-dsRNA has substantial sequence homology with the host viral genome and is not encapsidated in the coat protein of its helper virus, which represents a novel class of satellite-like nucleic acids, and it broadens the definition of satellite.

In this study, a novel positive-sense single-stranded RNA (+ssRNA) mycovirus, tentatively named Colletotrichum fructicola RNA virus 1 (CfRV1), was identified in the phytopathogenic fungus Colletotrichum fructicola. CfRV1 has seven genomic components, encoding seven proteins from open reading frames (ORFs) flanked by highly conserved untranslated regions (UTRs). Proteins encoded by ORFs 1, 2, 3, 5, and 6 are more similar to the putative RNA-dependent RNA polymerase (RdRp), hypothetical protein (P2), methyltransferase, and two hypothetical proteins of Hadaka virus 1 (HadV1), a capsidless 10- or 11-segmented +ssRNA virus, while proteins encoded by ORFs 4 and 7 showed no detectable similarity to any known proteins. Notably, proteins encoded by ORFs 1 to 3 also share considerably high similarity with the corresponding proteins of polymycoviruses. Phylogenetic analysis conducted based on the amino acid sequence of CfRV1 RdRp and related viruses placed CfRV1 and HadV1 together in the same clade, close to polymycoviruses and astroviruses. CfRV1-infected C. fructicola strains demonstrate a moderately attenuated growth rate and virulence compared to uninfected isolates. CfRV1 is capsidless and potentially encapsulated in vesicles inside fungal cells, as revealed by transmission electron microscopy. CfRV1 and HadV1 are +ssRNA mycoviruses closely related to polymycoviruses and astroviruses, represent a new linkage between +ssRNA viruses and the intermediate double-stranded RNA (dsRNA) polymycoviruses, and expand our understanding of virus diversity, taxonomy, evolution, and biological traits. IMPORTANCE A scenario proposing that dsRNA viruses evolved from +ssRNA viruses is still considered controversial due to intergroup knowledge gaps in virus diversity. Recently, polymycoviruses and hadakaviruses were found as intermediate dsRNA and +ssRNA stages, respectively, between +ssRNA and dsRNA viruses. Here, we identified a novel +ssRNA mycovirus, Colletotrichum fructicola RNA virus 1 (CfRV1), isolated from Colletotrichum fructicola in China. CfRV1 is phylogenetically related to the 10- or 11-segmented Hadaka virus 1 (HadV1) but consists of only seven genomic segments encoding two novel proteins. CfRV1 is naked and may be encapsulated in vesicles inside fungal cells, representing a potential novel lifestyle for multisegmented RNA viruses. CfRV1 and HadV1 are intermediate +ssRNA mycoviruses in the linkage between +ssRNA viruses and the intermediate dsRNA polymycoviruses and expand our understanding of virus diversity, taxonomy, and evolution.

Particulate-reinforced aluminum matrix composites are widely used owing to their advantageous comprehensive performance. For these composites, aging treatment is an important and essential process. However, researchers have discrepant opinions regarding the exact effects of particles on the aging behavior. In this study, the aging behavior of TiB2/2219Al composites is analyzed in terms of thermodynamics and kinetics. The results reveal that the particles can both promote aging and impede aging, and the peak aging times of the composites are advanced in this study. The effects of hybrid-sized TiB2 particles on the microstructures and mechanical properties of aged TiB2/2219Al composites are investigated. The results show noticeable dislocation propagation after the addition of TiB2, and this is confirmed by transmission electron microscopy observations and modified Williamson–Hall equation calculations. The Vickers hardness values are increased under all aging conditions. The strengths of the naturally aged composite, yield strength of the under-aged composite, and Young's modulus are increased significantly, whereas the strengths of composites under other aging conditions record only slight improvement. The total elongations of all the composites are decreased owing to the presence of TiB2 agglomerates.