Over a hundred years of research on plant viruses has led to a detailed understanding of viral replication, movement, and host–virus interactions. The functions of vast viral genes have also been annotated. With an increased understanding of plant viruses and plant–virus interactions, various viruses have been developed as vectors to modulate gene expressions for functional studies as well as for fulfilling the needs in biotechnology. These approaches are invaluable not only for molecular breeding and functional genomics studies related to pivotal agronomic traits, but also for the production of vaccines and health-promoting carotenoids. This review summarizes the latest progress in these forefronts as well as the available viral vectors for economically important crops and beyond.

Salicylic acid (SA) is a crucial hormone involved in plant immunity. Rice (Oryza sativa) maintains high SA levels that are not induced by pathogens. However, the roles of SA in rice immunity and yield remain largely unknown. Here, we identified SA 5-hydroxylases 1 (OsS5H1) and 2 (OsS5H2) as the primary enzymes engaged in catalysing SA to 2,5-dihydroxybenzoic acid (2,5-DHBA) in rice. SA levels were significantly increased in the oss5h mutants, while they were dramatically decreased in the OsS5H1 and OsS5H2 overexpression lines. The mutants were resistant, whereas the overexpression lines were susceptible to Pyricularia oryzae and Xanthomonas oryzae pv. Oryzae. Moreover, the pathogen-associated molecular patterns-triggered immunity responses, including reactive oxygen species burst and callose deposition, were enhanced in all the mutants and compromised in the overexpression lines. Quantification of the agronomic traits of the oss5h mutants grown in the paddy fields demonstrated that the grain number per panicle was decreased as the SA levels increased; however, the tiller number and grain size were enhanced, resulting in no significant yield penalty. Collectively, we reveal that mildly increasing SA content in rice can confer broad-spectrum resistance without yield penalty and put new insights into the roles of SA in immunity and growth.

Ustilaginoidea virens is the fungal pathogen causing rice false smut, resulting in not only yield lost but also grain pollution with toxic mycotoxins. Here we deployed PacBio Sequel II HIFI-read sequencing technology to generate a near-complete genome assembly for the U. virens isolate UV-FJ-1 (38.48 Mb), which was isolated from Fujian province, China. The genome assembly contains 116 contigs with N50 of 0.65 Mb and a maximum length of 2.10 Mb, and the genome completeness is ≥98% assessed by benchmarking universal single-copy orthologs (BUSCOs) and the mapping rate of Illumina short reads. Excluding 35.78% repeat sequences, we identified a total of 7,164 protein-coding genes, of which 5,818 were functionally annotated and 223 encode putative effector proteins. Moreover, 21 secondary metabolite biosynthesis gene clusters were found in UV-FJ-1 genome. Taken together, this high-quality genome assembly and gene annotation resource will provide a better insight for characterizing the biological and pathogenic mechanisms of U. virens.