Serine protease subtilase, found widely in both eukaryotes and prokaryotes, participates in various biological processes. However, how fungal subtilase regulates plant immunity is a major concern. Here, we identified a secreted fungal subtilase, UvPr1a, from the rice false smut (RFS) fungus Ustilaginoidea virens. We characterized UvPr1a as a virulence effector localized to the plant cytoplasm that inhibits plant cell death induced by Bax. Heterologous expression of UvPr1a in rice (Oryza sativa) enhanced plant susceptibility to rice pathogens. UvPr1a interacted with the important rice protein SUPPRESSOR OF G2 ALLELE OF skp1 (OsSGT1), a positive regulator of innate immunity against multiple rice pathogens, degrading OsSGT1 in a protease activity-dependent manner. Furthermore, host-induced gene silencing of UvPr1a compromised disease resistance of rice plants. Our work reveals a previously uncharacterized fungal virulence strategy in which a fungal pathogen secretes a subtilase to interfere with rice immunity through degradation of OsSGT1, thereby promoting infection. These genetic resources provide tools for introducing RFS resistance and further our understanding of plant–pathogen interactions.

Ustilaginoidea virens is an economically important biotrophic fungal pathogen that causes rice false smut worldwide. However, the regulatory mechanisms of smut ball formation under U. virens infection remain unclear. Here, we identified an important transcription factor, UvCom1, from this pathogen, which regulates the formation of smut balls on rice spikelets. UvCom1 contains two conserved internal repeat 1 (RPT) domains and is found only in fungi, with specific conservation in species of Basidiomycetes and Ascomycetes. UvCom1 protein N- or C-terminal fusion vectors both showed transactivation activity in yeast. Deletion of UvCom1 significantly affected the vegetative growth and conidiation of U. virens. UvCom1 negatively regulated the responses to oxidative, osmotic, and cell wall stresses. Remarkably, UvCom1 was found to be essential for the formation of rice smut balls, and UvCom1 deletion mutants lost the ability to stably utilize nutrients from the rice host. UvCom1 was also highly expressed at the mycelial expansion stage. Transcriptomic analysis and quantitative real-time PCR revealed that UvCom1 could affect the expression of genes significantly enriched in transmembrane transport. This study demonstrates that UvCom1 is a key transcription factor governing smut ball formation of this biotrophic fungus.

Bacterial soft rot caused by Pectobacterium species is a serious disease in konjac (Amorphophallus konjac), a healthy source of starch particularly in East Asia. An effective diagnostic method is crucial to control the disease and reduce losses in konjac production. In this study, we evaluated a loop-mediated isothermal amplification (LAMP) assay with a specific primer set for the rapid and accurate detection of P. aroidearum. A comparative genomics approach was used to identify the specific genes suitable for the design of LAMP primers. The candidate target genes were determined through a first-round comparison with a 50-genome nucleotide database, and subjected to a second-round screening with the GenBank NR database. As a result, nine specific genes of P. aroidearum were selected for LAMP primer design. After screening of the primers, the primer set 1675-1 was chosen for LAMP detection owing to its high specificity and sensitivity. The LAMP assay could detect the presence of P. aroidearum genomic DNA at a concentration as low as 50 fg and 1.2 × 10⁴ CFU/g artificially infected soil within 40 min at 65 °C. Subsequently, this primer set was successfully used to specifically detect P. aroidearum in naturally infected and non-symptomatic plant samples or soil samples from the field. This study indicates that a comparative genomic approach may facilitate the development of highly specific primers for LAMP assays, and a LAMP diagnostic assay with the specific primer set 1675-1 should contribute to the rapid and accurate detection of soft-rot disease in konjac at an early stage.