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MYB28 AND MYB29 shape ammonium stress responses by regulating Fe homeostasis

Although ammonium (NH4+) is a key intermediate of plant nitrogen metabolism, high concentrations of NH4+ in the soil provoke physiological disorders that lead to the development of stress symptoms.

Ammonium nutrition was shown to induce the accumulation of glucosinolates (GSLs) in leaves of different Brassicaceae species. To further understand the link between ammonium nutrition and GSLs, we analyzed the ammonium stress response of Arabidopsis mutants impaired in GSL metabolic pathway.

In this work, we show that the double knock-out mutant myb28myb29, which is almost deprived of aliphatic GSLs displays hypersensitivity to ammonium.Transcriptomic analysis highlighted the induction of iron (Fe) deficiency response in myb28myb29 under ammonium nutrition. Accordingly, ammonium‐grown myb28myb29 plants showed altered Fe accumulation and homeostasis. Interestingly, we show that growing Arabidopsis with increased Fe availability relieved ammonium stress symptoms and that this was associated with MYB28 and MYB29 expression. Overall, we evidence that MYB28 and MYB29 are key for Fe management under ammonium nutrition and that this function is independent of their known action as regulators of GSL metabolism.

• Taken together, our data indicate that the control of Fe homeostasis is crucial for Arabidopsis response to ammonium nutrition and evidence that MYB28 and MYB29 play a role in this control.

Figure. Transcriptome analysis of myb28myb29 plants grown with 5 mM NH4+ (a) Venn diagrams showing the number of up- and down-regulated genes in shoots and roots. Enriched categories for biological process of differentially expressed genes in in shoots (p ≤ 0.05).Working model for the role of MYB28 and MYB29 under ammonium nutrition.

Original Paper:

Coleto, I., Bejarano, I., Marín‐Peña, A.J., Medina, J., Rioja, C., Burow, M., Marino, D. 2020. Arabidopsis thaliana transcription factors MYB28 AND MYB29 shape ammonium stress responses by regulating fe homeostasis. New Phytologist. DOI: 10.1111/nph.16918

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