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Ras GTPase‐activating proteins (Ras GAPs) act as negative regulators for Ras proteins and are involved in various signalling processes that influence cellular functions. Here, the function of four Ras GAPs, UvGap1 to UvGap4, was identified and analysed in Ustilaginoidea virens, the causal agent of rice false smut disease. Disruption of UvGAP1 or UvGAP2 resulted in reduced mycelial growth and an increased percentage of larger or dumbbell‐shaped conidia. Notably, the mutant ΔUvgap1 completely lost its pathogenicity. Compared to the wild‐type strain, the mutants ΔUvgap1, ΔUvgap2 and ΔUvgap3 exhibited reduced tolerance to H2O2 oxidative stress. In particular, the ΔUvgap1 mutant was barely able to grow on the H2O2 plate, and UvGAP1 was found to influence the expression level of genes involved in reactive oxygen species synthesis and scavenging. The intracellular cAMP level in the ΔUvgap1 mutant was elevated, as UvGap1 plays an important role in maintaining the intracellular cAMP level by affecting the expression of phosphodiesterases, which are linked to cAMP degradation in U. virens. In a yeast two‐hybrid assay, UvRas1 and UvRasGef (Ras guanyl nucleotide exchange factor) physically interacted with UvGap1. UvRas2 was identified as an interacting partner of UvGap1 through a bimolecular fluorescence complementation assay and affinity capture‐mass spectrometry analysis. Taken together, these findings suggest that the UvGAP1‐mediated Ras pathway is essential for the development and pathogenicity of U. virens. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Summary: Pyricularia oryzae is a multi‐host pathogen causing cereal disease, including the devastating rice blast. Panicle blast is a serious stage, leading to severe yield loss. Thirty‐one isolates (average 4.1%) were collected from the rice panicle lesions at nine locations covering Jiangsu province from 2010 to 2017. These isolates were characterized as Pyricularia sp. jiangsuensis distinct from known Pyricularia species. The representative strain 18‐2 can infect rice panicle, root and five kinds of grasses. Intriguingly, strain 18‐2 can co‐infect rice leaf with P. oryzae Guy11. The whole genome of P. sp. jiangsuensis 18‐2 was sequenced. Nine effectors were distributed in translocation or inversion region, which may link to the rapid evolution of effectors. Twenty‐one homologues of known blast‐effectors were identified in strain 18‐2, seven effectors including the homologues of SLP1, BAS2, BAS113, CDIP2/3, MoHEG16 and Avr‐Pi54, were upregulated in the sample of inoculated panicle with strain 18‐2 at 24 hpi compared with inoculation at 8 hpi. Our results provide evidences that P. sp. jiangsuensis represents an addition to the mycobiota of blast disease. This study advances our understanding of the pathogenicity of P. sp. jiangsuensis to hosts, which sheds new light on the adaptability in the co‐evolution of pathogen and host. [ABSTRACT FROM AUTHOR]

Rice false smut caused by Villosiclava virens is one of the destructive diseases on panicles of rice. Sexual development of V. virens, controlled by mating-type locus, plays an important role in the prevalence of rice false smut and genetic diversity of the pathogen. However, how the mating-type genes mediate sexual development of the V. virens remains largely unknown. In this study, we characterized the two mating-type genes, MAT1-1-1 and MAT1-1-2, in V. virens. MAT1-1-1 knockout mutant showed defects in hyphal growth, conidia morphogenesis, sexual development, and increase in the tolerance to salt and osmotic stress. Targeted deletion of MAT1-1-2 not only impaired the sclerotia formation and pathogenicity of V. virens, but also reduced the production of conidia. The MAT1-1-2 mutant showed increases in tolerance to salt and hydrogen peroxide stress, but decreases in tolerance to osmotic stress. Yeast two-hybrid assay showed that MAT1-1-1 interacted with MAT1-1-2, indicating that those proteins might form a complex to regulate sexual development. In addition, MAT1-1-1 localized in the nucleus, and MAT1-1-2 localized in the cytoplasm. Collectively, our results demonstrate that MAT1-1-1 and MAT1-1-2 play important roles in the conidiation, stress response, sexual development, and pathogenicity of V. virens, thus providing new insights into the function of mating-type gene. [ABSTRACT FROM AUTHOR]

BACKGROUND Rice blast fungus is a worldwide disease, and it is one of the most serious rice diseases in the north and south rice fields in China. The initial symptoms of rice blast are not obvious, and the speed of transmission is fast. Manual identification is time‐consuming and laborious. At present, it is a great challenge to realize rapid and accurate early identification of rice blast. RESULTS: In this paper, an identification method based on crop disease spores' diffraction fingerprint texture for rice blast was studied; this method utilizes the light field and texture features of diffraction images. To verify the reliability of the model that we proposed, we selected two methods of manual identification and machine recognition to compare and detect rice blast spores. The experimental results show that the identification of light diffraction characteristics is not only higher than the traditional manual recognition by microscope (increased by more than 0.3%), but also faster after neural network training (increased by more than 90%). The diffraction recognition method used in this study, based on crop disease spores' diffraction fingerprint texture, can be completed in a few seconds, and its test accuracy is 97.18%. CONCLUSION: The proposed method, a rapid rice blast detection and identification method based on crop disease spores' diffraction fingerprint texture, has certain advantages compared with the existing manual identification by microscope. This method can be applied to the recognition of rice blast in agricultural research. © 2020 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Summary: The biotrophic fungal pathogen Ustilaginoidea virens causes rice false smut, a newly emerging plant disease that has become epidemic worldwide in recent years. The U. virens genome encodes many putative effector proteins that, based on the study of other pathosystems, could play an essential role in fungal virulence. However, few studies have been reported on virulence functions of individual U. virens effectors. Here, we report our identification and characterization of the secreted cysteine‐rich protein SCRE1, which is an essential virulence effector in U. virens. When SCRE1 was heterologously expressed in Magnaporthe oryzae, the protein was secreted and translocated into plant cells during infection. SCRE1 suppresses the immunity‐associated hypersensitive response in the nonhost plant Nicotiana benthamiana. Induced expression of SCRE1 in rice also inhibits pattern‐triggered immunity and enhances disease susceptibility to rice bacterial and fungal pathogens. The immunosuppressive activity is localized to a small peptide region that contains an important 'cysteine‐proline‐alanine‐arginine‐serine' motif. Furthermore, the scre1 knockout mutant generated using the CRISPR/Cas9 system is attenuated in U. virens virulence to rice, which is greatly complemented by the full‐length SCRE1 gene. Collectively, this study indicates that the effector SCRE1 is able to inhibit host immunity and is required for full virulence of U. virens. [ABSTRACT FROM AUTHOR]