Time-Resolved Investigation of Molecular Components Involved in the Induction of NO3- High Affinity Transport System in Maize Roots

The induction, i.e., the rapid increase of nitrate (NO3-,) uptake following the exposure of roots to the anion, was studied integrating physiological and molecular levels in maize roots. Responses to NO3- treatment were characterized in terms of changes in NO3- 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 similar to 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 NO3- 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.