Lopinski Philipp L, Schulz Christin, Fischer Alicia, Reichl Nadine, Engelsdorf Timo, Braun Nadja, Voll Lars M
Department Biology, Molecular Plant Physiology, Marburg University, Marburg, Germany.
Microcosm Earth Center, Marburg University, Marburg, Germany.
Mol Plant Pathol. 2025 Sep;26(9):e70148. doi: 10.1111/mpp.70148.
In previous work, we have shown that the transcription factor Nit2 plays a major role in the utilisation of non-favoured nitrogen sources like nitrate, minor amino acids or nucleobases in saprotrophic sporidia of the basidiomycete corn smut fungus Ustilago maydis. Addressing the knowledge gap regarding how filamentous phytopathogens adapt to nitrogen limitation in the host plant, we employed Δnit2 mutants in the natural FB1 × FB2 background to identify Nit2-regulated genes during biotrophy. We further investigated the impact of Nit2 on the physiology of leaf galls in nitrogen-replete versus nitrogen-limited host plants by comparative RNA-Seq and metabolic steady state analysis. About one third of the fungal genes affected by Nit2 during biotrophy were involved in nitrogen metabolism and transport, only showing minor overlap to saprotrophic sporidia. Induction of the nitrate assimilation cluster was completely dependent on Nit2 during biotrophy. In nitrogen-limited host plants, Δnit2 leaf galls accumulated nitrate and showed reduced accumulation of the nitrogen-rich phloem transport amino acids asparagine and glutamine compared to wild-type galls. However, total protein content in galls and pathogenicity were comparable between fungal genotypes in both nitrogen regimes. The findings of our physiological and transcriptomic analysis demonstrate that nitrate utilisation is dispensable for U. maydis during biotrophy and can likely be actively compensated by increased utilisation of abundant organic nitrogen sources, like asparagine, GABA and glutamine in a partially Nit2-dependent fashion.
在之前的研究中，我们已经表明转录因子Nit2在担子菌玉米黑粉菌Ustilago maydis的腐生担孢子利用硝酸盐、次要氨基酸或核碱基等非优势氮源的过程中发挥着主要作用。为了解决丝状植物病原体如何适应宿主植物中氮限制这一知识空白，我们在天然FB1×FB2背景下使用Δnit2突变体来鉴定生物营养过程中Nit2调控的基因。我们通过比较RNA测序和代谢稳态分析，进一步研究了Nit2在氮充足与氮限制宿主植物中对叶瘿生理的影响。在生物营养过程中受Nit2影响的真菌基因中，约三分之一参与氮代谢和转运，与腐生担孢子仅有少量重叠。在生物营养过程中，硝酸盐同化簇的诱导完全依赖于Nit2。在氮限制的宿主植物中，与野生型叶瘿相比，Δnit2叶瘿积累硝酸盐，并且富含氮的韧皮部运输氨基酸天冬酰胺和谷氨酰胺的积累减少。然而，在两种氮条件下，真菌基因型之间叶瘿中的总蛋白质含量和致病性相当。我们的生理和转录组分析结果表明，在生物营养过程中，硝酸盐利用对于玉米黑粉菌来说并非必需，并且很可能可以通过以部分依赖Nit2的方式增加对丰富有机氮源（如天冬酰胺、γ-氨基丁酸和谷氨酰胺）的利用来积极补偿。
