SNARE Molecules inMarchantia polymorpha: Unique and Conserved Features of the Membrane Fusion Machinery

Abstract

The membrane trafficking pathway has been diversified in a specific way for each eukaryotic lineage, probably to fulfill specific functions in the organisms. In green plants, comparative genomics has supported the possibility that terrestrialization and/or multicellularization could be associated with the elaboration and diversification of membrane trafficking pathways, which have been accomplished by an expansion of the numbers of genes required for machinery components of membrane trafficking, including soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins. However, information regarding membrane trafficking pathways in basal land plant lineages remains limited. In the present study, we conducted extensive analyses of SNARE molecules, which mediate membrane fusion between target membranes and transport vesicles or donor organelles, in the liverwort, Marchantia polymorpha. The M. polymorpha genome contained at least 34 genes for 36 SNARE proteins, comprising fundamental sets of SNARE proteins that are shared among land plant lineages with low degrees of redundancy. We examined the subcellular distribution of a major portion of these SNARE proteins by expressing Citrine-tagged SNARE proteins in M. polymorpha, and the results showed that some of the SNARE proteins were targeted to different compartments from their orthologous products in Arabidopsis thaliana. For example, MpSYP12B was localized to the surface of the oil body, which is a unique organelle in liverworts. Furthermore, we identified three VAMP72 members with distinctive structural characteristics, whose N-terminal extensions contain consensus sequences for N-myristoylation. These results suggest that M. polymorpha has acquired unique membrane trafficking pathways associated with newly acquired machinery components during evolution.

Functional PTB phosphate transporters are present in streptophyte algae and early diverging land plants

“…To test the hypothesis that core PTB proteins traffic to the plasma membrane through the secretory pathway, we expressed an MpPTB6‐YFP fusion protein in M. polymorpha . YFP fluorescence location was identical to that of the plasma membrane marker mCitrine‐MpSYP12A (Kanazawa et al ., ) and the ER marker YFP‐HDEL (Teh & Moore, ) in 25% and 75%, respectively, of plants expressing MpPTB6‐YFP (Fig. S5).…”

Switching secretory pathway direction for organelle acquisition in plants

“…Distinct from the other MpSYP1 members, MpSYP12B exhibits specific expression in oil body cells and localizes to the oil body membrane 10 . Oil body cells expressing a pro Mp SYP12B: 2×YFP construct indicated that MpSYP12B distributed around meristematic regions in young thalli, which was observed using light-sheet microscopy (Fig.…”

“…About 90% of liverwort species have this organelle; however, its origin, biogenesis, and physiological function remain unclear with controversial origins proposed from microscopic observations 6–9 . Through the systematic analysis of SNARE proteins in the liverwort, Marchantia polymorpha (hereafter referred to as Marchantia), we identified an oil body-resident protein, MpSYP12B 10 , which is a homolog of animal Syntaxin 1 that acts in the final step of exocytosis. Functions of SYP1 members to which MpSYP12B belongs dramatically diversified during plant evolution, suggesting expanded secretory trafficking systems in plants.…”

“…The SYP13 group mediates constitutive secretion, whereas the other groups are involved in plant-specific higher ordered functions; for example, KNOLLE/SYP111 is specifically involved in membrane fusion at forming cell plates, and PEN1/SYP121 is required for intact penetration resistance against powdery mildew fungi and regulation of the ion channel activity 11–16 . For more insight into the functional diversification of SYP1 members in Marchantia and the mechanism of oil body biogenesis, we further characterized four SYP1 members in this organism 10, 17 .…”

Systematic tools for reprogramming plant gene expression in a simple model,Marchantia polymorpha

“…There are two versions of the 35S promoter that are used in Marchantia: p5-35S 16,47 and p5-35Sx2 20 . Both of them have a strong activity in all parts of the gemmae and thallus except the notch area, where its activity is weak, and the oil body cells, where it is not active 48 (Figure 5B, 6C). On the other hand, the MpEF1α promoter is expressed in all parts of the thallus, but it is especially strong at the notch area 46 (Figure 5C, 6D).…”