Rice false smut, caused by Ustilaginoidea virens, is one of the most important diseases in rice. The disease not only causes significant yield losses in China and worldwide but also produces multiple types of mycotoxins that pose a serious threat to the health of humans and animals. To effectively prevent and control the disease, the pathogenicity mechanisms of U. virens have been studied preliminarily, and some control strategies have been developed. This review focuses on recent progress in understanding the molecular mechanisms of U. virens pathogenicity, including virulence-related genes, transcriptional regulation of virulence genes, and effector-mediated interactions between rice and U. virens. Based on the molecular mechanisms underlying the rice-U. virens interactions, the possibilities of the pathogenicity genes in U. virens and host immune-related genes as potential targets for biological agents, host-induced gene silencing, and molecular design breeding are also discussed.

Whole-genome duplication is a significant evolutionary mechanism in plants, with polyploid plants often displaying larger organs and enhanced adaptability to unfavorable conditions compared to their diploid counterparts. The cell wall acts as a primary defense for plant cells against external stresses, playing an essential role in the plant’s resistance to various stressors. In this study, we utilized both autotetraploid and its donor diploid rice (Oryza sativa L.) to analyze their phenotypic differences comparatively, the composition of key cell wall components, and the expression of related genes under normal conditions, as well as under stress from Magnaporthe oryzae (M. oryzae) and salt. Our findings indicated that autotetraploid rice exhibits significantly larger phenotypic characteristics under normal conditions than diploid rice. At the seedling stage, the lignin, cellulose, hemicellulose, and pectin levels in autotetraploid rice were markedly lower than in diploid rice. Additionally, 24 genes associated with major cell wall components showed differential expression between diploid and tetraploid rice. At the filling stage, the lignin and pectin content in autotetraploid rice were significantly higher than in diploid rice, while the levels of cellulose and hemicellulose were notably lower. Under M. oryzae stress or salt stress, autotetraploid rice showed smaller lesion areas and less wilting than diploid rice. The increased lignin content in autotetraploid rice under M. oryzae stress suggested a stronger adaptive capacity to adverse conditions. Compared to salt stress, M. oryzae stress induced more differential expression of genes related to major cell wall components. In this study, we explored the differences in the major cell wall components of diploid and homologous tetraploid rice under various treatment conditions. This study provides valuable insights into understanding the cell wall’s adaptive mechanisms in autotetraploid rice when facing blast disease and salt stress, and it reveals the differential gene expression linked to these adaptive capabilities.

Rice production faces new challenges from emerging diseases due to intensive cultivation practices and climate warming in China. A new rice leaf bacterial disease has recently occurred in Northeast China. The symptoms of the disease are similar to those of bacterial leaf blight. Disease lesions spread along leaf edges and are later dried up due to water loss. In this study, 17 bacterial isolates were identified as the causal agents of the new disease following Koch’s postulates. These strains are categorized into two groups based on colony morphology and molecular characterization. Phylogenetic analysis using the five housekeeping genes leuS, gyrB, fusA, pyrG, and rplB reveals that the two groups of the isolates belong to Pantoea ananatis and P. eucalypti, respectively. The new rice disease is caused by P. ananatis, P. eucalypti, or a combination of both bacterial species. A complete genome map has also been assembled for P. eucalypti. Meanwhile, some important virulence factors have been predicted based on gene annotation and determination of extracellular enzymes. Collectively, this study represents the first report of a new rice leaf disease caused by P. eucalypti and the first high-quality genome assembly of P. eucalypti that infects rice leaves.

The necessity to understand plant adaptations to environmental stressors is underscored by the role of polyploidy in species evolution. This study focuses on the superior stress resistance exhibited by autotetraploid rice, which arises from chromosome doubling, in comparison to its diploid donor. We provide a quantitative analysis that highlights the differing susceptibilities of diploid (GFD-2X) and autotetraploid (GFD-4X) rice to rice blast disease, with GFD-2X being significantly more susceptible. Our investigation centers on transcription factors (TFs), which are crucial in regulating biological stress responses, by analyzing their expression in the face of a pathogen attack. This study uncovers variations in the number and expression timing of differentially expressed TF genes, providing a quantitative view of GFD-4X’s resistance. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses confirm the role of specific pathways, including “response to stimulus” and the “MAPK signaling pathway,” in resistance mechanisms. An extensive analysis of protein–protein interaction networks further clarifies the complex role of TFs during stress responses. The rationale for our experimental approach is rooted in the imperative to decipher the molecular basis of disease resistance across different ploidies, which has implications for crop enhancement. The conclusion from our research is that autotetraploid rice has a unique and more effective defense response regulation system, facilitated by transcription factors, when faced with rice blast disease. This finding provides a foundation for future genetic strategies aimed at improving crop resistance.

Ustilaginoidin D is a type of bis-naphtho-γ-pyrone mycotoxin produced by Ustilaginoidea virens, the causal agent of rice false smut. Although previous studies have demonstrated the inhibitory effect of ustilaginoidin D on ATP synthesis and cancer cell growth in mice, its specific health risks remain unclear. Here, we reveal that ustilaginoidin D is highly toxic to mice with an LD₅₀ value of 213 mg /kg·bw. Dose-dependent weight loss and liver damage were observed, accompanied by altered markers of liver cell damage, including the enzyme activities of alanine aminotransferase and aspartate aminotransferase and the content of glutathione in mouse liver. RNA-seq analysis of liver tissues from mice treated with 150 mg of ustilaginoidin D/kg·bw identified significant changes in gene expression profiles, with differentially expressed genes enriched in cancer-related pathways, hypertrophic cardiomyopathy, and metabolic pathways. RT-qPCR data are highly consistent with transcriptome analysis in expression profiles of 22 chemical-carcinogenesis-associated genes. These findings indicate that ustilaginoidin D induces acute toxicity and liver dysfunction in mice, raising serious concerns about its threat to human health.

Frogeye leaf spot (FLS), caused by Cercospora sojina, is a significant disease affecting soybean crops economically. Seed inspection plays a vital role in reducing the incidence of this disease. However, limited research has been conducted on the fast and accurate identification of C. sojina in soybean seeds. In this study, we developed a rapid diagnostic method to detect C. sojina in soybean seeds using loop-mediated isothermal amplification (LAMP) assays. A software application called K-mer Elimination by Cross-reference was utilized to identify specific sequences belonging to C. sojina. The LAMP primer set designed based on the selected specific sequence proved to be highly specific, distinguishing C. sojina from other common soybean pathogens and two maize pathogens of the Cercospora genus. The primer set exhibited remarkable sensitivity, detecting sixteen copies per reaction, which is approximately 1,000 times more sensitive than conventional PCR. The LAMP assays were applied for direct inspection of soybean seeds, revealing that twenty of the thirty tested soybean varieties were contaminated with C. sojina, with contamination rates ranging from 10% to 60%. The seeds of TongNong 943 and JiNong 38 had the highest contamination rate at 60%. Seeds coated with fungicide showed a reduced disease incidence, as demonstrated on PDA medium and in soil pots. In summary, our results indicate that rapid seed diagnosis using LAMP assays can effectively screen out seeds carrying C. sojina, providing a preventive strategy in managing FLS disease.