In light of these observations, we concluded that a low oxygen niche is indeed established in the late stages of primordium development. LRP developmental progression was not assessed in the frame of this experiment, due to the impossibility of attributing the stage of each LRP before and after the treatments. β-glucuronidase (GUS) staining in the LRP and the surrounding pericycle and vasculature was observed after stage IV under aerobic conditions, but could be moved up to earlier stages by hypoxic conditions or almost entirely abolished when plants were, in contrast, treated with hyperoxia for 48 h ( Figure 1D). PromPCO1: GFP-GUS plants were grown vertically on agarized MS plates in normoxia (21% O 2 V/V) and treated for 4 days with hypoxia (1% O 2 V/V) or hyperoxia (80% O 2 V/V). To assess whether induction of the hypoxia-responsive genes was caused by reduced oxygen availability in the LRP, or rather by a developmental program, we decided to observe the activity of our transcriptional reporters for hypoxia in LRPs exposed to different oxygen concentrations. Our results support a model in which the establishment of hypoxic niches in the developing lateral root primordia contributes to the shutting down of key auxin-induced genes and regulates the production of lateral roots. ERF-VIIs repress the expression of the auxin-induced genes LBD16, LBD18, and PUCHI, which are essential for lateral root development, by binding to their promoters. Using gain- and loss-of-function mutants, we show that ERF-VII transcription factors, which mediate hypoxic responses, control root architecture by acting in cells with a high level of auxin signaling. Here, we report that such niches are established at specific stages of lateral root primordia development in Arabidopsis thaliana grown under aerobic conditions. Establishment of hypoxic niches in the developing tissues of plants has been postulated as a consequence of insufficient diffusion of oxygen to satisfy the demands throughout development. As non-photosynthesizing organs, roots are dependent on diffusion of oxygen from the external environment and, in some instances, from the shoot for their aerobic metabolism.

Root primordia tomato plant