ABSTRACT

The fungus Sarocladium oryzae (Sawada) causes rice sheath rot and produces the phytotoxins cerulenin and helvolic acid. Both toxins show antimicrobial activity but only helvolic acid production in the rice sheath correlates with virulence. Sarocladium oryzae isolates that differ in their toxin production were used to study their interaction with the rice culturable bacterial endophyte community. The diversity and community structure was defined in the edge of sheath rot lesions, followed by a null model-based co-occurrence analysis to discover pairwise interactions. Non-random pairs were co-cultured to study the nature of the interactions and the role of the toxins herein. Compared to healthy sheaths, endophyte diversity strongly increased when infected with the least virulent S. oryzae isolates producing low amounts of toxins. Virulent S. oryzae isolates did not affect diversity but caused strong shifts in species composition. The endophyte community of healthy rice plants was dominated by B. cereus. This bacterium was enriched in lesions produced by low-virulent S. oryzae isolates and caused hyphal lysis. Contrarily, helvolic acid producers eliminated this bacterium from the sheath endosphere. We conclude that S. oryzae needs to produce antibiotics to defend itself against antagonistic rice endophytes to successfully colonize and infect the rice sheath.

中文翻译：

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优胜劣汰：水稻微生物群落如何迫使米曲霉致病性

摘要

稻米Sarocladium oryzae（Sawada）真菌会引起水稻鞘腐烂，并产生植物毒素铜绿素和硬脂酸。两种毒素均显示出抗菌活性，但仅水稻鞘中产生的羟乙酸与毒力相关。使用毒素生产不同的米曲霉菌株来研究其与水稻可培养细菌内生菌群落的相互作用。在鞘腐病病灶的边缘定义了多样性和群落结构，随后进行了基于空模型的共现分析以发现成对相互作用。共培养非随机对，以研究相互作用的性质和本文毒素的作用。与健康鞘相比，感染最弱的细菌会强烈增加内生菌的多样性米曲霉分离株产生少量毒素。有毒的米曲霉菌株不会影响多样性，但会导致物种组成发生强烈变化。健康水稻植物的内生菌群落以蜡状芽孢杆菌为主。该细菌富含低毒米曲霉分离物产生的损伤，并引起菌丝裂解。相反，乙醇酸生产者从鞘内球中消除了这种细菌。我们得出的结论是，米曲霉需要生产抗生素来防御自身拮抗的水稻内生菌，才能成功地定殖并感染水稻鞘。