Structure-function relationship between plastid morphology and carbon partitioning during secondary cell wall synthesis in Arabidopsis thaliana

Abstract

A VND7 induction system in Arabidopsis was used to study plastid morphology at different time points during secondary cell wall deposition. We analyzed published transcriptomic and metabolic data to contextualize these morphological changes to construct an integrated view of plastid biology during xylogenesis. This provided insight into how xyloplasts are morphologically distinct from other non-green plastids and how their structure reflects their function. The expression of VND7 was induced using dexamethasone in 7-day VND7-inducible Arabidopsis thaliana seedlings at different time points. Transmission electron microscopy was performed to study leaf cross-sections. The NExylo application was used to analyse published Arabidopsis thaliana VND7 vessel induction data. The xyloplast (2-2.5 μm) is a unique plastid found in xylem vessels which contains electron-dense contents but lacks starch granules and an inner membrane system. It plays a role in rapid Phe synthesis, which enters the monolignol synthetic pathway for lignification preceding and followed by PCD. Vessel element induction results in major ultrastructural changes in chloroplasts, with an intermediate morphology typical of plastid differentiation, supporting the existence of the xyloplast. Integration of morphology and gene expression analysis showed that carbon partitioning linked to plastid terminal differentiation and degradation play a key role in xylogenesis.