A well-known physiological adaptation process of plants encountering drying soil 
is to achieve water balance by reducing shoot growth and maintaining or 
promoting root elongation, but little is known about the molecular basis of this 
process. This study investigated the role of a drought-up-regulated Triticum 
aestivum NAC69-1 (TaNAC69-1) in the modulation of root growth in wheat. 
TaNAC69-1 was predominantly expressed in wheat roots at the early vegetative 
stage. Overexpression of TaNAC69-1 in wheat roots using OsRSP3 (essentially 
root-specific) and OsPIP2;3 (root-predominant) promoters resulted in enhanced 
primary seminal root length and a marked increase in maturity root biomass. 
Competitive growth analysis under water-limited conditions showed that OsRSP3 
promoter-driven TaNAC69-1 transgenic lines produced 32% and 35% more 
above-ground biomass and grains than wild-type plants, respectively. TaNAC69-1 
overexpression in the roots down-regulated the expression of TaSHY2 and TaIAA7, 
which are from the auxin/IAA (Aux/IAA) transcriptional repressor gene family and 
are the homologs of negative root growth regulators SHY2/IAA3 and IAA7 in 
Arabidopsis. The expression of TaSHY2 and TaIAA7 in roots was down-regulated by 
drought stress and up-regulated by cytokinin treatment, which inhibited root 
growth. DNA binding and transient expression analyses revealed that TaNAC69-1 
bound to the promoters of TaSHY2 and TaIAA7, acted as a transcriptional 
repressor and repressed the expression of reporter genes driven by the TaSHY2 or 
TaIAA7 promoter. These data suggest that TaNAC69-1 is a transcriptional 
repressor of TaSHY2 and TaIAA7 homologous to Arabidopsis negative root growth 
regulators and is likely to be involved in promoting root elongation in drying 
soil.