A newly identified virus in the family potyviridae encodes two leader cysteine proteases in tandem that evolved contrasting RNA silencing suppression functions

Potyviridae is the largest family of plant-infecting RNA viruses and includes many agriculturally and economically important viral pathogens. The viruses in the family, known as potyvirids, possess single-stranded, positive-sense RNA genomes with polyprotein processing as a gene expression strategy. The N-terminal regions of potyvirid polyproteins vary greatly in sequence. Previously, we identified a novel virus species within the family, Areca palm necrotic spindle-spot virus (ANSSV), which was predicted to encode two cysteine proteases, HCPro1 and HCPro2, in tandem at the N-terminal region. Here, we present evidence showing self-cleavage activity of these two proteins and define their cis-cleavage sites. We demonstrate that HCPro2 is a viral suppressor of RNA silencing (VSR), and both the variable N-terminal and conserved C-terminal (protease domain) moieties have antisilencing activity. Intriguingly, the N-terminal region of HCPro1 also has RNA silencing suppression activity, which is, however, suppressed by its C-terminal protease domain, leading to the functional divergence of HCPro1 and HCPro2 in RNA silencing suppression. Moreover, the deletion of HCPro1 or HCPro2 in a newly created infectious clone abolishes viral infection, and the deletion mutants cannot be rescued by addition of corresponding counterparts of a potyvirus. Altogether, these data suggest that the two closely related leader proteases of ANSSV have evolved differential and essential functions to concertedly maintain viral viability.This work is supported by grants from the Hainan Major Research Fund of Science and Technology (ZDKJ201817), the National Natural Science Foundation of China (32060603), and the Central Public-interest Scientific Institution Basal Research Fund for the Chinese Academy of Tropical Agricultural Sciences (grant no. 19CXTD-33).Peer reviewe

Development of novel specific molecular markers for the Sw-5b gene to assist with tomato spotted wilt virus-resistant tomato breeding

Abstract Tomato spotted wilt virus (TSWV) is a plant pathogen that causes devastating tomato yield losses worldwide. The Sw-5b gene is one of the most effective resistance genes for TSWV control in tomato plants, and has been widely used in resistance breeding. Molecular markers are specific DNA sequences with known locations on the chromosome; they are indispensable tools in marker-assisted selection, which detects the presence of target genes to expedite breeding. We developed gene-specific molecular markers for Sw-5b to facilitate the accurate distinction of resistance (Sw-5b R ) and susceptibility (Sw-5b S ) alleles of Sw-5b. Using these markers, we successfully detected Sw-5b and determined its genotype (homozygous Sw-5b R , heterozygous Sw-5b R/S , or homozygous Sw-5b S ) in six tomato varieties. Then we successfully applied these markers to 46 commercial tomato cultivars to detect and determine the genotype of Sw-5b. The results revealed a striking absence of the Sw-5b R gene and high TSWV susceptibility among most of the analyzed commercial cultivars. With the assistance of the novel Sw-5b-specific molecular markers, we generated a TSWV-resistant and homozygous Sw-5b R Micro-Tom tomato line, demonstrating the practical application of these markers in plant breeding. In summary, we developed novel gene-specific molecular markers for Sw-5b, and applied them to distinguish Sw-5b alleles for TSWV resistance or susceptibility. This marker set provides a valuable tool for breeding TSWV-resistant tomato varieties