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Poster

Session: Session 2 Presenting Authors at Posters (Evens)

P-266 - The Ustilago maydis transcription factor Nit2 regulates nitrate utilization during biotrophy and influences organic nitrogen metabolism in infected maize leaves under nitrogen limitation

Thursday, July 17, 2025
13:30 - 15:15  
Location: Confex Hall 3
Nutrient exchange & role of metabolites in plant-microbe interactions

Little is known on how filamentous phytopathogens adapt to nitrogen limitation in the host plant. In previous work, we have shown that the transcription factor Nit2 plays a major role for the utilization of non-favored nitrogen sources like nitrate, minor amino acids or nucleobases in saprotrophic sporidia of the basidiomycete corn smut fungus Ustilago maydis.
Here, we employed Δnit2 mutants in the natural FB1 x FB2 background to identify Nit2 regulated genes during biotrophy and investigated the impact of Nit2 on the physiology of leaf galls in nitrogen replete versus nitrogen limited host plants. RNA-Seq analysis of galls revealed that about one third of the genes affected by Nit2 deletion during fungal biotrophy are involved in nitrogen metabolism and transport. Induction of the nitrate assimilation cluster was completely dependent on Nit2 in nitrogen deplete host plants.Hence, leaf galls caused by Δnit2 accumulated more nitrate than wild type galls and showed reduced accumulation of the nitrogen-rich phloem transport amino acids asparagine and glutamine. Since total protein content in galls and fungal virulence were comparable between genotypes and in both nitrogen regimes, our findings demonstrate that nitrate utilization is dispensable for Ustilago maydis during biotrophy. RNA-Seq data and steady state metabolite analysis suggest that utilization of abundant organic nitrogen sources can compensate for this limitation in a partially Nit2-dependent fashion.