Zinc triggers a complex transcriptional and post-transcriptional regulation of the metal homeostasis geneFRD3inArabidopsisrelatives

InArabidopsis thaliana,FRD3(FERRIC CHELATE REDUCTASE DEFECTIVE 3) plays a central role in metal homeostasis.FRD3is among a set of metal homeostasis genes that are constitutively highly expressed in roots and shoots ofArabidopsis halleri, a zinc hyperaccumulating and hypertolerant species. Here, we examined the regulation ofFRD3by zinc in both species to shed light on the evolutionary processes underlying the evolution of hyperaccumulation inA. halleri. We combined gene expression studies with the use of β-glucuronidase and green fluorescent protein reporter constructs to compare the expression profile and transcriptional and post-transcriptional regulation ofFRD3in both species. TheAtFRD3andAhFRD3genes displayed a conserved expression profile. InA. thaliana, alternative transcription initiation sites from two promoters determined transcript variants that were differentially regulated by zinc supply in roots and shoots to favour the most highly translated variant under zinc-excess conditions. InA. halleri, a single transcript variant with higher transcript stability and enhanced translation has been maintained. TheFRD3gene thus undergoes complex transcriptional and post-transcriptional regulation inArabidopsisrelatives. Our study reveals that a diverse set of mechanisms underlie increased gene dosage in theA. hallerilineage and illustrates how an environmental challenge can alter gene regulation.