The insect pathogenic fungus, Metarhizium anisopliae is a commercialized microbial agent used in biological control efforts targeting a diverse range of agricultural and other insect pests. The second step in the synthesis of a group of M. anisopliae α-pyrone diterpenoids (termed subglutinols) involves the activity of a prenyltransferase family geranylgeranyl diphosphate synthase (product of the subD/MaGGPPS5 gene). Here, we show that targeted gene disruption of MaGGPPS5 results in earlier conidial germination and faster greater vegetative growth compared to the wild type (WT) parent and complemented strains. In addition, insect bioassays revealed that the ΔMaGGPPS5 mutant strain displayed significantly increased virulence, with a ~50% decrease in the mean lethal time (LT₅₀, from 6 to 3 days) to kill (50% of) target insects, and an ~15–40-fold decrease in the mean lethal dose (LC₅₀). Metabolite profiling indicated increased accumulation in the ΔMaGGPPS5 mutant of select subglutinols (A, B and C) and destruxins (A, A2, B and B2), the latter a set of fungal secondary metabolites that act as insect toxins, with a concomitant loss of production of subglutinol ‘analogue 45’. These data suggest that the increased virulence phenotype seen for the ΔMaGGPPS5 strain can, at least in part, be attributed to a combination of faster growth and increased insect toxin production, linking the production of two different secondary metabolite pathways, and represent a novel approach for the screening of isolates with enhanced virulence via modulation of terpenoid secondary metabolite biosynthesis.

中文翻译：

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异戊二烯基转移酶的突变导致 subglutinols 和 destruxins 的积累和昆虫病原体绿僵菌的毒力增强

昆虫病原真菌绿僵菌是一种商业化的微生物制剂，用于针对多种农业和其他害虫的生物防治工作。第二步合成一组M。anisopliae α-pyrone diterpenoids（称为 subglutinols）涉及异戊二烯基转移酶家族香叶基香叶基二磷酸合酶（subD / MaGGPPS5基因的产物）的活性。在这里，我们表明，与野生型 (WT) 亲本和互补菌株相比， MaGGPPS 5 的靶向基因破坏导致更早的分生孢子萌发和更快的营养生长。此外，昆虫生物测定表明，Δ MaGGPPS5突变株的毒力显着增加，杀死（50%）目标昆虫的平均致死时间（LT ₅₀，从 6 到 3 天）减少约 50%，平均致死时间减少约 15-40 倍致死剂量（LC ₅₀）。代谢物分析表明 Δ MaGGPPS5突变体中选择的 subglutinol（A、B 和 C）和 destruxins（A、A2、B 和 B2）的积累增加，后者是一组充当昆虫毒素的真菌次生代谢物，伴随着损失生产 subglutinol '类似物 45'。这些数据表明 Δ MaGGPPS5的毒力表型增加菌株至少部分可归因于更快的生长和增加的昆虫毒素产生的组合，将两种不同次生代谢物途径的产生联系起来，并代表了一种通过调节萜类次级代谢物来筛选具有增强毒力的分离物的新方法代谢物生物合成。