Functions of the Plant Qbc SNARE SNAP25 in Cytokinesis and Biotic and Abiotic Stress Responses

Abstract

Eukaryotes transport biomolecules between intracellular organelles and between cells and the environment via vesicle trafficking. Soluble N -ethylmaleimide-sensitive factor attachment protein receptors (SNARE proteins) play pivotal roles in vesicle and membrane trafficking. These proteins are categorized as Qa, Qb, Qc, and R SNAREs and form a complex that induces vesicle fusion for targeting of vesicle cargos. As the core components of the SNARE complex, the SNAP25 Qbc SNAREs perform various functions related to cellular homeostasis. The Arabidopsis thaliana SNAP25 homolog AtSNAP33 interacts with Qa and R SNAREs and plays a key role in cytokinesis and in triggering innate immune responses. However, other Arabidopsis SNAP25 homologs, such as AtSNAP29 and AtSNAP30, are not well studied; this includes their localization, interactions, structures, and functions. Here, we discuss three biological functions of plant SNAP25 orthologs in the context of AtSNAP33 and highlight recent findings on SNAP25 orthologs in various plants. We propose future directions for determining the roles of the less well-characterized AtSNAP29 and AtSNAP30 proteins.

Keywords: Qbc SNARE; SNAP25; abiotic stress responses; cytokinesis; innate immune response.

Fig. 1. Phylogenetic tree of SNAP25 proteins in plants.

Phylogenetic analysis was performed using MEGAX software (Kumar et al.,2018) with full amino acid sequences of the retrieved SNAP25 proteins from public databases; UniProt, GenBank, Sol Genomics, and Phytozome, and additionally only functionally studied SNAP25 proteins from G. soja, H. vulgare, T. aestivum, G. hirsutum, and C. komarovii. The bootstrap values from 1000 replicates are depicted at the nodes. Different colors indicate the following: green, Brassicaceae; red, Solanaceae; blue, Fabaceae; violet, Poaceae; black, other functionally reported SNAP25 proteins. All information in the tree is described in Table 1

Fig. 2. Structure of SNAP25 in humans.

SNAP25 proteins comprise a coiled-coil of the Qb domain at the N-terminus, a linker region, and a coiled-coil of the Qc domain at the C-terminus. Images were prepared by SWISS-MODEL, an automated protein structure homology-modeling server, using SNAP25 protein from humans (UniProtKB - P60880) (Waterhouse et al., 2018).