CLAVATA modulates auxin homeostasis to regulate stem cell identity in a moss (New Phytol.)

The size and shape of aerial organs in angiosperms is determined by the activity of shoot apical meristem cells. The mechanism by which this cell population is maintained has been well described in Arabidopsis, and involves a negative feedback loop of diffusible CLAVATA peptides and the transcription factor WUSCHEL. However, in bryophytes WUSCHEL is not essential for stem cell maintenance, posing questions about the evolutionary origins of stem cell regulation in the last common ancestor of land plants. In this study, Nemec-Venza et al. show that in the moss Physcomitrium patens, CLAVATA genes regulate stem cell identity by altering the activity of the plant hormone auxin. The group utilized plants with knock-out mutations in CLAVATA family genes alongside chemical modulators of auxin activity to unravel the complex interplay between these two pathways. Through this approach, they identified the receptor-like kinase PpRPK2 as the key regulator of stem cell identity and organ shape via its effect on auxin homeostasis. The authors thus suggest that the regulatory network consisting of CLAVATA, auxin and stem cell function is conserved across land plants, while the WUSCHEL gene family was incorporated into the pathway following the emergence of vascular plants. (Summary by Rory Burke @rorby95) New Phytol. 10.1111/nph.17969