Agrobacterium-Mediated Genetic Transformation of the Edible and Medicinal Cauliflower Mushroom Sparassis latifolia

Sparassis latifolia is an edible and medicinal mushroom with significant economic value, now commercially cultivated on a large scale in China. However, current cultivars face challenges, including an extended mycelial growth period and unstable fruiting body yields. Advances in molecular breeding and functional genomics for this species are hindered by the absence of a reliable genetic transformation system. In this study, we first determined that S. latifolia is highly sensitive to carboxin and hygromycin, two selective agents commonly used in fungal genetics. We subsequently constructed a novel binary vector, pCbxHyg, harboring a carboxin resistance cassette driven by its native Pleurotus eryngii promoter and a hygromycin resistance cassette under the control of the P. eryngii Glycerol 3-phosphate dehydrogenase (GPD) gene promoter. Initial transformation attempts using Agrobacterium-mediated transformation of liquid-cultured mycelial pellets were unsuccessful. During microscopic examination, we discovered that S. latifolia mycelia produce abundant asexual chlamydospores. Using these chlamydospores as recipient material, we efficiently and reproducibly obtained transformants with the pCbxHyg vector under both carboxin and hygromycin selection. This method highlights the advantage of using asexual spores of Basidiomycetes as recipients for genetic transformation. PCR analysis confirmed the stable integration of the exogenous resistance genes into the fungal genome. The functionality of the system was further validated by transforming chlamydospores with a vector carrying a β-glucuronidase (GUS) reporter gene, whose expression was confirmed via histochemical staining of the resulting transformant mycelia. This work establishes the first successful Agrobacterium-mediated genetic transformation system for S. latifolia, providing a foundational platform for future gene function studies and molecular breeding efforts.