Low oxygen levels are needed to regulate shoot meristem activity (Nature)

Little is known about the stimuli that regulate time intervals for new leaves production (plastochrone) at the shoot apical meristem (SAM). Oxygen is a diffusible molecule with potential to regulate this process. The use of a micro-scale Clark-type oxygen electrode allowed Weits et al. to measure oxygen at the SAM. A low oxygen niche was found around the stem-cells and hyperoxic (80% O2) conditions reduced SAM activity as shown by using a hypoxia responsive promoter. Weits and co-workers also searched for SAM related proteins that were a target of the oxygen branch of the N-degron pathway, and LITTLE ZIPPER2 (ZPR2) was identified. ZPR2-GUS reporter lines showed that hypoxia indeed inhibited the proteolysis by the N-degron pathway, and ZPR2 mutants showed a decreased leaf production compared to the wild type. ZPR members are known to be negative regulators of HD-ZIP III transcription factors and further experiments showed that ZPR2 repressed the activity and interacted with REVOLUTA (REV), PHABULOSA (PHB) and HOMEOBOX GENE 8 (ATHB8). (Summary by Cecilia Vasquez-Robinet)  Nature 10.1038/s41586-019-1203-6