Under phosphate starvation conditions, Fe and Al trigger accumulation of the transcription factor STOP1 in the nucleus of Arabidopsis root cells
Résumé
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.
Origine : Publication financée par une institution
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