Rice blast, caused by Pyricularia oryzae, is one of the most destructive rice diseases worldwide. Using resistant rice varieties is the most cost-effective way to control the disease, and it is crucial to analyze the resistance level and the resistance genes distribution of the main varieties. In this study, we collected 119 rice main varieties in Jiangsu province and evaluated the resistance to leaf and panicle blast and found that indica rice was more resistant to rice blast than japonica rice. Moreover, we detected the distribution of 14 resistance genes (R genes) in the 119 varieties. The distribution frequencies of three R genes, Pish, Pit, and Pia, were higher than 80%, and the Pigm had the lowest distribution frequency (1.68%), followed by Pi2 (15.18%) and Pi5, Piz-t (24.37%). Combined with the multiple stepwise regression and the resistance contribution rate, eight major R genes Pita, Pi5, Pi9, Pib, Pb1, Pikm, Piz-t, and Pi2 significantly affected the resistance of rice, and we also found that six gene combinations with 100% resistance contribution rate could effectively increase the resistance of rice varieties. In summary, monitoring the resistance level of rice varieties and analyzing their resistance genes were beneficial for rice resistance breeding.

Rice false smut, caused by Ustilaginoidea virens, is a serious disease of rice worldwide, severely reducing the quantity and quality of rice production. The conserved fungal velvet proteins are global regulators of diverse cellular processes. We identified and functionally characterized two velvet genes, UvVEA and UvVELB, in U. virens. The deletion of these genes affected the conidiation of U. virens but had no effect on the virulence of this pathogen. Interestingly, the ΔUvVEA mutants appeared in the form of smaller false smut balls with a reduced number of chlamydospores compared with the wide-type strains. In addition, the deletion of UvVEA affected the expression of some transmembrane transport genes during chlamydospore formation and rice false smut balls development. Furthermore, the ΔUvVEA mutants were shown to be defective in the utilization of glucose. These findings proved the regulatory mechanism underlying the formation of rice false smut balls and chlamydospores and provided a basis for the further exploration of the mechanism of these processes.

The mitogen-activated protein kinase (MAPK) signaling pathways regulate diverse cellular processes and have been partially characterized in the rice false smut fungus Ustilaginoidea virens. UvSte50 has been identified as a homolog to Saccharomyces cerevisiae Ste50, which is known to be an adaptor protein for MAPK cascades. ΔUvste50 was found to be defective in conidiation, sensitive to hyperosmotic and oxidative stresses, and non-pathogenic. The mycelial expansion of ΔUvste50 inside spikelets of rice terminated at stamen filaments, eventually resulting in a lack of formation of false smut balls on spikelets. We determined that UvSte50 directly interacts with both UvSte7 (MAPK kinase; MEK) and UvSte11 (MAPK kinase kinase; MEKK), where the Ras-association (RA) domain of UvSte50 is indispensable for its interaction with UvSte7. UvSte50 also interacts with UvHog1, a MAP kinase of the Hog1-MAPK pathway, which is known to have important roles in hyphal growth and stress responses in U. virens. In addition, affinity capture–mass spectrometry analysis and yeast two-hybrid assay were conducted, through which we identified the interactions of UvSte50 with UvRas2, UvAc1 (adenylate cyclase), and UvCap1 (cyclase-associated protein), key components of the Ras/cAMP signaling pathway in U. virens. Together, UvSte50 functions as an adaptor protein interacting with multiple components of the MAPK and Ras/cAMP signaling pathways, thus playing critical role in plant infection by U. virens.

Rice blast, caused by Pyricularia oryzae, is one of the most destructive rice diseases worldwide. Using resistant rice varieties is the most cost-effective way to control rice blast. Consequently, it is critical to monitor the distribution frequency of avirulence (Avr) genes in rice planting fields to facilitate the breeding of resistant rice varieties. In this study, we established a rapid recombinase polymerase amplification–lateral flow dipstick (RPA-LFD) detection system for the identification of AvrPik, Avr-Piz-t, and Avr-Pi9. The optimized reaction temperature and duration were 37°C and 20 min, indicating that the reaction system could be initiated by body temperature without relying on any precision instruments. Specificity analysis showed that the primer and probe combinations targeting the three Avr genes exhibited a remarkable specificity at genus-level detection. Under the optimized condition, the lower detected thresholds of AvrPik, Avr-Piz-t, and Avr-Pi9 were 10 fg/μl, 100 fg/μl, and 10 pg/μl, respectively. Notably, the detection sensitivity of the three Avr genes was much higher than that of PCR. In addition, we also successfully detected the presence of AvrPik, Avr-Piz-t, and Avr-Pi9 in the leaf and panicle blast lesions with the RPA-LFD detection system. In particular, the genomic DNA was extracted using the simpler PEG-NaOH rapid extraction method. In summary, we developed an RPA detection system for AvrPik, Avr-Pi9, and Avr-Piz-t, combined with the PEG-NaOH rapid DNA extraction method. The innovative approach achieved rapid, real-time, and accurate detection of the three Avr genes in the field, which is helpful to understand the distribution frequency of the three Avr genes in the field and provide theoretical reference for the scientific layout of resistant rice varieties.

Rice blast, caused by Pyricularia oryzae, is one of the most destructive rice diseases worldwide. It is essential to understand the population structure and race distribution of P. oryzae for the prevention and control of rice blast. This study collected 1584 isolates across Jiangsu province from 2003 to 2017 to determine race diversity, common and dominant race structures, and resistance profiles using eight parameters from the Chinese differential cultivars (CDC) entries. Race diversity analysis indicated that the race diversity of 1584 isolates in Jiangsu province increased from 2003 to 2006 and fluctuated steadily from 2007 to 2017. Common race structure analysis showed that the common race structure of the isolates fluctuated wildly on an annual basis. Moreover, the race ZG1 was the dominant race, suggesting that the most commonly grown rice varieties in Jiangsu are highly adaptive to race ZG1. In addition, due to a higher level (>85%) of resistance to the population of isolates from 2003 to 2017, Tetep may be conformed as the most promising donor of blast resistance for resistance breeding in Jiangsu province. In summary, it is beneficial to control rice blast by continuous monitoring of the population structure and distribution of P. oryzae with the monogenic germplasm entries and by maintaining a diversity of rice varieties.

Rice false smut (RFS), caused by Ustilaginoidea virens (teleomorph: Villosiclava virens), is a devastating fungal disease that severely impacts global rice production by reducing both yield and grain quality. While the mating-type gene UvMAT1-1-3 is known to regulate both sexual and asexual reproduction in U. virens, its regulatory mechanism remains unclear. In this study, an interacting protein of UvMAT1-1-3, a putative O-methyltransferase (UvPomt), was identified using yeast two-hybrid screening, and its interaction was further confirmed by co-localization microscopy. A quantitative reverse transcription PCR (qRT-PCR) analysis showed a significant up-regulation of UvPomt expression during the early infection stage of U. virens. Functional characterization revealed that ΔUvPomt mutants exhibited reduced fungal pathogenicity, vegetative growth, conidial production, and stress adaptation. Furthermore, a Western blot analysis revealed that the UvMAT1-1-3 protein level was reduced in ΔUvPomt mutants, whereas the UvPomt protein level was elevated in ΔUvMAT1-1-3 mutants. Taken together, these findings suggest a potential reciprocal regulation between UvPomt and UvMAT1-1-3. Understanding UvPomt’s function could provide a potential molecular target for controlling RFS disease.