Exploring the formation and permeability of plasmodesmata in the liverwort, <i>Marchantia polymorpha</i>

Plasmodesmata are cell-wall-embedded channels that evolved in the common ancestor of land plants to increase cell-to-cell communication. Whether all the fundamental properties of plasmodesmata emerged and were inherited in all land plants at the same time is unknown. Here, we show that the bryophyte Marchantia polymorpha (a nonvascular plant) forms mostly simple plasmodesmata in early-developing gemmae. The complexity of plasmodesmata increases during gemma maturation, and complex plasmodesmata with enlarged cavities are majorly observed in thalli. In contrast to vascular plants, whose simple plasmodesmata can transport monomeric fluorescent proteins, plasmodesmata in M. polymorpha limited their permeability before the juvenile-to-adult transition. In support, callose, a known polysaccharide regulating plasmodesmata permeability in vascular plants, accumulated in most of the M. polymorpha tissues examined. Furthermore, we found that in the apical meristematic region, plasmodesmata allowed the transport of monomeric fluorescent proteins, and this relaxation might correlate with the lower accumulation of callose. Taken together, our study suggests that certain plasmodesmata properties, such as complexity progression and callose accumulation, may have evolved before the divergence between vascular and nonvascular plants.