Regulation of Arabidopsis root system architecture by oxygen availability

Postembryonic development of lateral roots (LRs) in plants, a major determinant of root architecture, is controlled by genetic and environmental factors to optimize nutrient acquisition in a heterogeneous and changing environment. Among other environmental cues, oxygen levels potentially direct root architectural variations. A decrease in oxygen availability is known to cause root growth inhibition in Arabidopsis, although this is mainly considered to be associated to reduced metabolic rates. Group-VII ethylene response factors (ERFs) control the cellular low oxygen response by regulation of respiration. However, when constitutively stabilized, these TFs can impact on plant development, suggesting their involvement in additional biological functions. Here, we dissect the role of ERFVII factors in hormonal regulation of lateral root (LR) development. We identified specific hormonal pathways at play under low oxygen stress by exploiting accessible microarray data on hypoxic Arabidopsis roots. Amid other hormones, jasmonic acid (JA) alongside auxin, appeared to be the most interesting, owing to its actual role in root developmental processes. With the aid of hormone responsive reporters for JA (Jas9-VENUS) and auxin (DR5-GFP), we displayed the activity of JA and auxin under hypoxia in primary and secondary root meristems. Phenotypic data from over-expressor and mutant plants suggested the specific role of these TFs in controlling root architecture in Arabidopsis thaliana. Differential expression profiles of genes responsible for root development under low oxygen stress and in erfVII mutants provide evidence of inhibition of LR developmental genes due to ERF-VII activity. Our findings reveal a novel role of group ERF-VII TFs in the definition of root architecture in A. thaliana.