Auxins are hormones that regulate growth and development in plants. Besides plants, various microorganisms also produce auxins. Here we investigate whether and how the phytopathogenic fungus Leptosphaeria maculans biosynthesizes auxins. We characterized the auxin profile of in vitro grown L. maculans. The culture was further supplied with the auxin biosynthetic-precursors tryptophan and tryptamine and gene expression and phytohormone content was analyzed. L. maculans in vitro produced IAA (indole-3-acetic acid) as the predominant auxin metabolite. IAA production could be further stimulated by supplying precursors. Expression of indole-3-pyruvate decarboxylase LmIPDC2, tryptophan aminotransferase LmTAM1 and nitrilase LmNIT1 genes was mainly upregulated after adding tryptophan and correlated with IAA production, suggesting that these genes are the key components of auxin biosynthesis in L. maculans. Tryptamine acted as a potent inducer of IAA production, though a pathway independent of LmIPDC2/LmTAM1 may be involved. Despite L. maculans being a rich source of bioactive IAA, the auxin metabolic profile of host plant Brassica napus was not altered upon infection. Exogenous IAA inhibited the growth of L. maculans in vitro when supplied in high concentration. Altogether, we showed that L. maculans is capable of IAA production and we have identified biosynthetic genes that were responsive to tryptophan treatment.

生长素是调节植物生长发育的激素。除植物外，各种微生物还产生生长素。在这里，我们调查是否以及如何致病性真菌黄褐线虫生物合成植物生长素。我们表征了体外生长的L. maculans的生长素谱。向培养物进一步提供植物生长素生物合成前体色氨酸和色胺，并分析基因表达和植物激素含量。黄斑狼疮在体外产生IAA（吲哚-3-乙酸）作为主要的生长素代谢产物。供应前体可进一步刺激IAA的生产。吲哚-3-丙酮酸脱羧酶LmIPDC2，色氨酸转氨酶的表达LmTAM1和腈水解LmNIT1基因主要是上调加入色氨酸后，用IAA生产相关，这表明这些基因在植物生长素的生物合成的关键部件L. maculans。虽然可能涉及一个独立于LmIPDC2 / LmTAM1的途径，但色胺可作为IAA产生的有效诱导剂。尽管黄斑狼疮是富含生物活性IAA的来源，但宿主植物甘蓝型油菜的生长素代谢特征在感染后并未改变。当以高浓度提供时，外源IAA在体外抑制了黄斑狼疮的生长。总而言之，我们证明了黄斑狼疮 能够产生IAA，我们已经鉴定出对色氨酸处理有反应的生物合成基因。