What’s up with stromules?

Stromules are stroma-filled tubules that extend from plant and algal plastids. Their formation is dynamic, and their abundance increases following many different stresses and hormone treatments, yet questions remain about their function. In a recent article, Rahpeyma et al. set about to understand the roles of stromules in cultured tobacco BY-2 cells. The article starts with a well-written overview summarizing out current understanding of stromule formation and function. The authors next explored two alternate hypotheses about stromule function; hormone synthesis and retrograde signaling. OPDA is synthesized in plastids, but it is converted to jasmonate in peroxisomes, so the authors investigated whether stromules serve to transfer OPDA between these organelles. Although they demonstrate that there is proximity between them, they favor the other model. Blocking stromule formation alters gene expression patterns and sensitivity to hormones, suggesting that the role of stromules is more aligned with retrograde signaling from plastid to nucleus rather than hormone synthesis. (Summary by Mary Williams @PlantTeaching.bsky.org) Plant Physiol. 10.1093/plphys/kiag373