Fungal dimorphism is a phenomenon by which a fungus can grow both as a yeast form and a hyphal form. It is frequently related to pathogenicity as different growth forms are more suitable for different functions during a life cycle. Among dimorphic plant pathogens, the corn smut fungus Ustilago maydis serves as a model organism to understand fungal dimorphism and its effect on pathogenicity. However, there is a lack of data on whether mechanisms elucidated from model species are broadly applicable to other fungi. In this study, two non-model plant-associated species in the smut fungus subphylum (Ustilaginomycotina), Tilletiopsis washingtonensis and Meira miltonrushii, were selected to compare dimorphic mechanisms in these to those in U. maydis. We sequenced transcriptomic profiles during both yeast and hyphal growth in these two species using Tween40, a lipid mimic, as a trigger for hyphal growth. We then compared our data with previously published data from U. maydis and a fourth but unrelated dimorphic phytopathogen, Ophiostoma novo-ulmi. Comparative transcriptomics was performed to identify common genes upregulated during hyphal growth in all four dimorphic species. Intriguingly, T. washingtonensis shares the least similarities of transcriptomic alteration (hyphal growth versus yeast growth) with the others, although it is closely related to M. miltonrushii and U. maydis. This suggests that phylogenetic relatedness is not correlated with transcriptomic similarity under the same biological phenomenon. Among commonly expressed genes in the four species, genes in cell energy production and conversion, amino acid transport and metabolism and cytoskeleton are significantly enriched. Considering dimorphism genes characterized in U. maydis, as well as hyphal tip-associated genes from the literature, we found only genes encoding the cell end marker Tea4/TeaC and the kinesin motor protein Kin3 concordantly expressed in all four species. This suggests a divergence in species-specific mechanisms for dimorphic transition and hyphal growth.

真菌二态性是一种真菌可以以酵母形式和菌丝形式生长的现象。它通常与致病性有关，因为不同的生长形式更适合生命周期中的不同功能。在二态性植物病原体中，玉米黑穗病菌Ustilago maydis作为模式生物来了解真菌二态性及其对致病性的影响。然而，缺乏从模型物种阐明的机制是否广泛适用于其他真菌的数据。在这项研究中，选择了黑穗病真菌亚门（黑穗病菌）中的两种非模式植物相关物种，华盛顿紫穗病菌和米氏梅拉菌，将这些物种的二态性机制与美国黑穗病菌的二态性机制进行比较. 我们使用 Tween40（一种脂质模拟物）作为菌丝生长的触发器，对这两个物种的酵母和菌丝生长过程中的转录组谱进行了测序。然后，我们将我们的数据与之前公布的来自U. maydis和第四种但不相关的双态植物病原体Ophiostoma novo-ulmi 的数据进行了比较。进行比较转录组学以鉴定所有四种双态物种在菌丝生长过程中上调的常见基因。有趣的是，尽管与M. miltonrushii和U. maydis密切相关，但T.华盛顿与其他物种在转录组学改变（菌丝生长与酵母生长）方面的相似性最少. 这表明在同一生物学现象下，系统发育相关性与转录组学相似性无关。在4个物种的常见表达基因中，细胞能量产生与转化、氨基酸转运与代谢、细胞骨架基因显着丰富。考虑到U. maydis 中表征的二态性基因，以及文献中的菌丝尖端相关基因，我们发现只有编码细胞末端标记Tea4/TeaC和驱动蛋白运动蛋白Kin3 的基因在所有四个物种中一致表达。这表明双态转变和菌丝生长的物种特异性机制存在分歧。