Molecular identification of a root apical cell-specific and stress-responsive enhancer from an Arabidopsis enhancer...

Plant root apex is the major part to direct the root growth and development by responding to various signals/cues from internal and soil environments. To study and understand root system biology particularly at a molecular and cellular level, an Arabidopsis T-DNA insertional enhancer trap line J3411 expressing reporters (GFP) only in the root tip was adopted in this study to isolate a DNA fragment.

Using nested PCR, DNA sequencing and sequence homology search, the T-DNA insertion site(s) and its flanking genes were characterised in J3411 line. Subsequently, a 2000 bp plant DNA-fragment (E_rtip1) upstream of the insert position of the coding T-DNA was in silico analysed, revealing certain putative promoter/enhancer cis-regulatory elements. Cloning and transformation of this DNA fragment and its truncated segments tagged with or without 35S minimal promoter (35Smini), all of which were fused with a GFP or GUS reporter, allowed to detect GFP and GUS expression mediated only by E_rtip1 + 35mini (P_{Ertip1+35Smini}) specifically in the Arabidopsis root tip region. The P_{Ertip1+35Smini} activity was further tested to be strong and stable under many different growth conditions but suppressed by cold, salt, alkaline pH and higher ammonium and phosphorus.

This work describes a promising strategy to isolate a tissue-/cell-specific enhancer sequence from the enhancer trap lines, which are publically available. The reported synthetic promoter i.e. P_{Ertip1+35Smini} may provide a valuable and potent molecular-tool for comprehensive investigation of a gene function related to root growth and development as well as molecular engineering of root-architectural formation aiming to improve plant growth.