Mechanical contribution of germ cell specification in Arabidopsis anthers.

A central question in developmental biology is how germ lines are established. We studied the specification of male germ cells (GCs) within the anther. Here, we focused on the potential role of mechanics, an aspect of anther development that has been very poorly characterized. Using a combination of live imaging and mechanical measurements, we showed that GCs emerge within a special micromechanical niche, where the inner tissues exert pressure on the outer cell layers, placing themselves under compression. Mechanical perturbations impair tissue expansion patterns and severely compromise GC specification. Further investigations revealed that the master genetic regulator SPOROCYTELESS/NOZZLE (SPL/NZZ) was central in establishing this micromechanical environment via cell wall softening. In turn, the mechanical cues stabilized the transcription of SPL/NZZ. Here, we propose an intrinsic growth-derived mechanochemical feedback loop that safeguards the fate of GCs.