RESUMEN
Commercial cultivation of the mushroom fungus, Agaricus bisporus, utilizes a substrate consisting of a lower layer of compost and upper layer of peat. Typically, the two layers are seeded with individual mycelial inoculants representing a single genotype of A. bisporus. Studies aimed at examining the potential of this fungal species as a heterologous protein expression system have revealed unexpected contributions of the mycelial inoculants in the morphogenesis of the fruiting body. These contributions were elucidated using a dual-inoculant method whereby the two layers were differientially inoculated with transgenic ß-glucuronidase (GUS) and wild-type (WT) lines. Surprisingly, use of a transgenic GUS line in the lower substrate and a WT line in the upper substrate yielded fruiting bodies expressing GUS activity while lacking the GUS transgene. Results of PCR and RT-PCR analyses for the GUS transgene and RNA transcript, respectively, suggested translocation of the GUS protein from the transgenic mycelium colonizing the lower layer into the fruiting body that developed exclusively from WT mycelium colonizing the upper layer. Effective translocation of the GUS protein depended on the use of a transgenic line in the lower layer in which the GUS gene was controlled by a vegetative mycelium-active promoter (laccase 2 and ß-actin), rather than a fruiting body-active promoter (hydrophobin A). GUS-expressing fruiting bodies lacking the GUS gene had a bonafide WT genotype, confirmed by the absence of stably inherited GUS and hygromycin phosphotransferase selectable marker activities in their derived basidiospores and mycelial tissue cultures. Differientially inoculating the two substrate layers with individual lines carrying the GUS gene controlled by different tissue-preferred promoters resulted in up to a â¼3.5-fold increase in GUS activity over that obtained with a single inoculant. Our findings support the existence of a previously undescribed phenomenon of long-distance protein translocation in A. bisporus that has potential application in recombinant protein expression and biotechnological approaches for crop improvement.
Asunto(s)
Agaricales/genética , Agaricus/genética , Transporte de Proteínas , Agaricales/metabolismo , Agaricus/metabolismo , ADN Complementario/metabolismo , Hongos/genética , Biblioteca de Genes , Genes Fúngicos , Modelos Biológicos , Morfogénesis/genética , Fenotipo , Reacción en Cadena de la Polimerasa , Regiones Promotoras Genéticas , Análisis de Secuencia de ADN , Esporas Fúngicas/genética , Transcripción Genética , TransgenesRESUMEN
We have devised an easy and effective genetic transformation method for the preeminent edible mushroom, Agaricus bisporus. Our method exploits the T-DNA transfer mechanism in Agrobacterium tumefaciens and relies on the reproductive fruiting body as the recipient tissue. The use of fruiting body explants, particularly the gill, provided high-frequency transformation, overcoming the inefficacy of Agrobacterium-based methods targeting fungal spores or vegetative mycelium. The protocol entails incubation of A. tumefaciens for 3 h with acetosyringone, a signaling molecule that launches the gene transfer mechanism, co-cultivation of the induced bacterium and gill explants for 3 d, and selection for transformants based on an inherited resistance to the antibiotic hygromycin. Between 7 and 28 d on the selection medium, upwards of 95% of the gill explants generate hygromycin-resistant colonies. About 75% of the mushroom transformants show a single-copy of the hygromycin-resistant gene integrated at random sites in the genome.