Trichoderma species play important roles in nature as plant growth promotors and antagonists of phytopathogenic fungi, and are used as models to study photomorphogenesis. Molecular tools have been implemented to manipulate and improve these fungi. However, instability of transformants or very low frequency of homologous recombination has been reported. Here, we report the fate of transforming DNA, demonstrating that it can follow two different fates. When a vector contains sequences also present in the Trichodermaatroviride genome, it mainly integrates by homologous recombination generating stable recombinant strains. In contrast, vectors with no sequence homology to the T. atroviride genome generate unstable transformants, losing the transforming DNA in the first generation of conidia produced without selection where, surprisingly, the vector behaves as autoreplicative. Integration by homologous recombination was demonstrated when transformants were generated with a truncated version of the blr2 gene, resulting in insertional mutants with phenotypes identical to those of knockout mutants. Our results indicate that T. atroviride is highly efficient in integrating DNA by homologous recombination and that plasmid vectors with no sequence homology to the genome are maintained for several generations in T. atroviride if kept under selective pressure even though they lacked fungal autonomous replication sequences.

中文翻译：

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强烈偏好通过同源重组整合转化 DNA 的木霉属 atroviride

木霉属物种在自然界中作为植物生长促进剂和植物病原真菌的拮抗剂发挥着重要作用，并被用作研究光形态发生的模型。已经实施了分子工具来操纵和改进这些真菌。然而，已经报道了转化体的不稳定性或非常低的同源重组频率。在这里，我们报告了转化 DNA 的命运，证明它可以遵循两种不同的命运。当载体包含也存在于木霉病毒基因组中的序列时，它主要通过产生稳定重组菌株的同源重组进行整合。相比之下，与 T. atroviride 基因组没有序列同源性的载体会产生不稳定的转化体，在未经选择的情况下产生的第一代分生孢子中丢失转化 DNA，其中令人惊讶的是，该向量表现为自动复制。当用 blr2 基因的截短形式产生转化体时，同源重组的整合被证明，导致插入突变体的表型与敲除突变体相同。我们的结果表明，T. atroviride 在通过同源重组整合 DNA 方面非常有效，并且如果保持在选择压力下，即使它们缺乏真菌自主复制序列，与基因组没有序列同源性的质粒载体仍可在 T. atroviride 中保持几代。