Time-resolved investigation of molecular components involved in the induction of NO-3 high affinity transport system in maize roots

The induction, i.e., the rapid increase of nitrate (NO-3) uptake following the exposure of roots to the anion, was studied integrating physiological and molecular levels in maize roots. Responses to NO-3 treatment were characterized in terms of changes in NO-3 uptake rate and plasma membrane (PM) H+-ATPase activity and related to transcriptional and protein profiles of NRT2, NRT3, and PM H+-ATPase gene families. The behavior of transcripts and proteins of ZmNRT2s and ZmNRT3s suggested that the regulation of the activity of inducible high-affinity transport system (iHATS) is mainly based on the transcriptional/translational modulation of the accessory protein ZmNRT3.1A. Furthermore, ZmNRT2.1 and ZmNRT3.1A appear to be associated in a ~150 kDa oligomer. The expression trend during the induction of the 11 identified PM H+-ATPase transcripts indicates that those mainly involved in the response to NO-3 treatment are ZmHA2 and ZmHA4. Yet, partial correlation between the gene expression, protein levels and enzyme activity suggests an involvement of post-transcriptional and post-translational mechanisms of regulation. A non-denaturing Deriphat-PAGE approach allowed demonstrating for the first time that PM H+-ATPase can occur in vivo as hexameric complex together with the already described monomeric and dimeric forms.