Under phosphate starvation conditions, Fe and Al trigger accumulation of the transcription factor STOP1 in the nucleus of Arabidopsis root cells

Christian Godon 1 Caroline Mercier 1 Xiaoyue Wang 2 Pascale David 1 Pierre Richaud 3 Laurent Nussaume 1 Dong Liu 2, * Thierry Desnos 1, *
* Corresponding author
1 SAVE - Signalisation de l'Adaptation des Végétaux à l'Environnement
BIAM - Institut de Biosciences et Biotechnologies d'Aix-Marseille (ex-IBEB) : DRF/BIAM
3 EBM - Bioénergie et Microalgues
BIAM - Institut de Biosciences et Biotechnologies d'Aix-Marseille (ex-IBEB) : DRF/BIAM
Abstract : Low-phosphate (Pi) condition is known to repress the primary root growth of Arabidopsis, in a low-pH and Fe-dependent manner. This growth arrest requires the accumulation of STOP1 transcription factor in the nucleus where it activates the transcription of the malate transporter gene ALMT1; exuded malate is suspected to interact with extracellular iron to inhibit root growth. In addition, ALS3 –an ABC-like transporter first identified for its role for tolerance to toxic aluminum– represses nuclear accumulation of STOP1 and the expression of ALMT1. Until now, it was unclear whether phosphate deficiency itself or iron activates STOP1 to accumulate in the nucleus. Here, by using different growth media to dissociate the effects of Fe from Pi deficiency itself, we demonstrate that Fe is sufficient to trigger the accumulation of STOP1 in the nucleus, which in turn, activates the expression of ALMT1. We also show that a low pH is necessary to stimulate the Fe-dependent accumulation of nuclear STOP1. Furthermore, pharmacological experiments indicate that Fe inhibits proteasomal degradation of STOP1. We also show that Al acts like Fe for nuclear STOP1 accumulation and ALMT1 expression, and that the overaccumulation of STOP1 in the nucleus of the als3 mutant grown in low-Pi could be abolished by Fe deficiency. Altogether, our results indicate that, under low-Pi condition, Fe$^{2/3+}$ and Al$^{3+}$ act similarly to increase the stability of STOP1 and its accumulation in the nucleus where it activates the expression of ALMT1.
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Christian Godon, Caroline Mercier, Xiaoyue Wang, Pascale David, Pierre Richaud, et al.. Under phosphate starvation conditions, Fe and Al trigger accumulation of the transcription factor STOP1 in the nucleus of Arabidopsis root cells. Plant Journal, Wiley, In press, ⟨10.1111/tpj.14374⟩. ⟨cea-02149165⟩

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