The Bax inhibitor UvBI-1, a negative regulator of mycelial growth and conidiation, mediates stress response and is critical for pathogenicity of the rice false smut fungus Ustilaginoidea virens
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Bax inhibitor-1 (BI-1), an evolutionarily conserved protein, is a suppressor of cell death induced by the proapoptotic protein Bax and is involved in the response to biotic and abiotic stress in animals, plants and yeast. Rice false smut caused by Ustilaginoidea virens is one of the destructive rice diseases worldwide. Although BI-1 proteins are widely distributed across filamentous fungi, few of them are functionally characterized. In this study, we identified a BI-1 protein in U. virens, UvBI-1, which contains a predicted Bax inhibitor-1-like family domain and could suppress the cell death induced by Bax. By co-transformation of the CRISPR/Cas9 construct along with donor DNA fragment containing the hygromycin resistance gene, we successfully generated Uvbi-1 deletion mutants. The UvBI-1 deletion showed an increase in mycelia vegetative growth and conidiation, suggesting this gene acts as a negative regulator of the growth and conidiation. In addition, the Uvbi-1 mutants exhibited higher sensitivity to osmotic and salt stress, hydrogen peroxide stress, and cell wall or membrane stress than the wild-type strain. Furthermore, UvBI-1 deletion was found to cause increased production of secondary metabolites and loss of pathogenicity of U. virens. Taken together, our results demonstrate that UvBI-1 plays a negative role in mycelial growth and conidiation, and is critical for stress tolerance, cell wall integrity, secondary metabolites production and pathogenicity of U. virens. Therefore, this study provides new evidence on the conserved function of BI-1 among fungal organisms and other species.
KeywordsBax inhibitor-1 Ustilaginoidea virens Hyphal growth Conidiation Stress response Secondary metabolites Pathogenicity
We thank JinRong Xu from Northwest A&F University, Yangling, China, and Purdue University, West Lafayette, IN, the United States, for the CRISPR-Cas9 system plasmid, Yuanchao Wang from Nanjing Agricultural University for the pGR107 vector and Bax and Daohong Jiang from Huazhong Agricultural University for the complemented vector PCETNS4. The National Natural Science Foundation of China (No. 31701736), the National Key Research and Development Program (2016YFD0300700) and the Fundamental Research Funds for the Central Universities (No. 2662017JC003 and 2662018JC051) supported this research.
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