Functional study of fusion protein SsUBA52 in the growth and development of Sclerotinia sclerotiorum

This study aimed to elucidate the biological function of the fusion protein SsUBA52 in the growth and development of Sclerotinia sclerotiorum. As a typical necrotrophic phytopathogenic fungus, S. sclerotiorum relies on the formation of sclerotia and compound appressoria as critical determinants of its high disease incidence and strong infectivity. In this study, we constructed SsUBA52-silenced and complementary strains to systematically investigate the regulatory role of this gene in the growth and development of S. sclerotiorum. Compared with the wild-type strain, the SsUBA52-silenced strains exhibited a significant reduction in both the number and weight of sclerotia, whereas the number of compound appressoria was markedly increased. Moreover, the silenced strains displayed enhanced infection capability on onion epidermis and significantly elevated pathogenicity on rapeseed leaves. Subcellular localization analysis revealed that SsUBA52 was distributed in both the cytoplasm and the nucleus. In addition, under various external stress conditions, the mycelial growth inhibition rate of the SsUBA52-silenced strains was significantly higher than that of the wild-type strain. Transcriptomic analysis further demonstrated that SsUBA52 not only participates in the ubiquitination cascade but also regulates ribosome synthesis and assembly, thereby engaging in crosstalk with the MAPK signaling pathway and the autophagy pathway. Further assays confirmed that SsUBA52 acts as a positive regulator of autophagy in S. sclerotiorum. Collectively, this study is the first to systematically reveal the multifaceted biological functions of SsUBA52 in S. sclerotiorum and its association with the autophagy pathway, providing a novel molecular target for further elucidation of the pathogenic mechanisms of this fungus.