Qa-SNAREs localized to the trans -Golgi network regulate multiple transport pathways and extracellular disease resistance in plants

Abstract

In all eukaryotic cells, a membrane-trafficking system connects the post-Golgi organelles, such as the trans-Golgi network (TGN), endosomes, vacuoles, and the plasma membrane. This complex network plays critical roles in several higher-order functions in multicellular organisms. The TGN, one of the important organelles for protein transport in the post-Golgi network, functions as a sorting station, where cargo proteins are directed to the appropriate post-Golgi compartments. Unlike its roles in animal and yeast cells, the TGN has also been reported to function like early endosomal compartments in plant cells. However, the physiological roles of the TGN functions in plants are not understood. Here, we report a study of the SYP4 group (SYP41, SYP42, and SYP43), which represents the plant orthologs of the Tlg2/syntaxin16 Qa-SNARE (soluble N-ethylmaleimide sensitive factor attachment protein receptor) that localizes on the TGN in yeast and animal cells. The SYP4 group regulates the secretory and vacuolar transport pathways in the post-Golgi network and maintains the morphology of the Golgi apparatus and TGN. Consistent with a secretory role, SYP4 proteins are required for extracellular resistance responses to a fungal pathogen. We also reveal a plant cell-specific higher-order role of the SYP4 group in the protection of chloroplasts from salicylic acid-dependent biotic stress.Arabidopsis | membrane traffic | membrane fusion I n eukaryotic cells, membrane fusion is an essential process in protein secretion and endocytosis (1, 2). Selective membrane fusion occurs with the concerted functions of several molecules, including SNAREs (soluble N-ethylmaleimide sensitive factor attachment protein receptors), Rab GTPases, tethering factors, and Sec1p/Munc18 (SM) proteins. SNAREs are membrane-anchored proteins that contain α-helical heptad repeats and a characteristic central amino acid within the SNARE motif. The SNARE complex comprises four SNAREs, including three with a central glutamine residue in SNARE motif (Q-SNAREs: Qa, Qb, and Qc) and one with a central arginine (R-SNARE) in SNARE motif. The Q-SNAREs reside on the target membrane, and the R-SNARE resides on the transport vesicle. This complex first forms a bridge between the target organelle membrane and the vesicle, and then compresses to bring the two membranes close enough to mediate specific membrane fusion. After fusion is complete, the SNARE complex is dissociated by a NSF (N-ethylmaleimide-sensitive factor), and the SNAREs are recycled. To execute the correct membrane fusion, SNAREs must be localized on the membrane of specific organelles or transport vesicles. QaSNAREs also serve as organelle markers (3-5), by virtue of their specific localization on the membrane of target organelles.The TGN was first defined as a special organelle on the transside of the Golgi stack that is responsible for protein sorting to the plasma membrane or lysosomes (6). The TGN contains multiple sorting domains and functions as the compartment of cargo sorting. In addition, the TGN ...

The KEEP ON GOING Protein of Arabidopsis Regulates Intracellular Protein Trafficking and Is Degraded during Fungal Infection

“…HopM interactor7 is an ADP ribosylation factor guanine nucleotide exchange factor protein and has been shown to modulate vesicle trafficking and polar deposition of callose in response to infection by bacterial pathogens (Nomura et al, 2006(Nomura et al, , 2011. Similarly, SYP42 and SYP43, TGN/EE-localized Q-SNARE proteins, play important but redundant roles in secretion, vacuolar transport, and resistance to a fungal pathogen (Aoyama and Chua, 1997;Brocard et al, 2002;Uemura et al, 2012).…”

Involvement of Adapter Protein Complex 4 in Hypersensitive Cell Death Induced by Avirulent Bacteria

“…Interestingly, OsVAMP7, a rice (Oryza sativa) SNARE localized to the vacuolar membrane, is suggested to play a role in resistance to blast disease (Sugano et al, 2016). In addition, SNARE proteins involved in plant immune responses have also been reported, although they are mostly associated with the plasma membrane (Collins et al, 2003;Kalde et al, 2007;Uemura et al, 2012). Future identification of the cargo proteins of the AP-4 complex may provide clues about the molecular mechanism underlying membrane fusion and its regulation of HR cell death during ETI.…”

The physiological role of SYP4 in the salinity and osmotic stress tolerances

“…This chlorosis was dependent on an intact pathogen-inducible salicylic acid biosynthesis pathway. 4 However, the physiological functions of SYP4 in abiotic stress have not yet been reported.…”

“…[1][2][3] Recently, we reported the higher-order functions of the trans-Golgi network (TGN)-localized Qa-SNAREs, the SYP4 group consisting of SYP41, SYP42, and SYP43 in Arabidopsis. 4 Individual single homozygous mutants (syp41, syp42, and syp43) were fully viable, but triple homozygous mutants (syp41…”

“…In our original paper, [4] syp42syp43 was mainly analyzed because this mutant is not lethal, though it does exhibit the dwarf and early senescence phenotypes. Since each single mutant for SYP41, SYP42, and SYP43 showed no abnormal phenotypes in abiotic stress response (data not shown), we analyzed syp42syp43 mutants in this study.…”