In most plants, callose is a rare cell wall polymer. Yet, in various developmental or adaptive contexts, it accumulates at specific sites in the cell wall to high levels. Callose deposition is famously plastic and both deposition and degradation can occur rapidly and repeatedly upon developmental or abiotic and biotic cues. In plants, callose synthases belong to a family of very large proteins with a conserved overall structure and a central glucan-synthase like domain. Yet, despite their role in important developmental and adaptive processes, we are still largely ignorant in which way callose synthases (CALS) differ from each other and which characteristics make them essential to a specific process.

We previously showed that CALS7 is localized around sieve pores, the cytosolic connections between sieve elements in the phloem and where it is essential during development (Kalmbach et al. 2023, PMID: 36805125). Using callose deposition around phloem sieve pores as a system, we are dissecting whether callose synthases are interchangeable, which features may confer specificity to defined developmental and/or adaptive processes, and which cellular processes may affect enzyme recruitment and callose biosynthesis.