Abstract
Soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins mediate intracellular vesicle fusion, which is an essential cellular process of the eukaryotic cells. To investigate the role of SNARE proteins in the rice blast fungus Magnaporthe oryzae, MoSec22, an ortholog of Saccharomyces cerevisiae SNARE protein Sec22, was identified and the MoSEC22 gene disrupted. MoSec22 restored a S. cerevisiae sec22 mutant in resistance to cell wall perturbing agents, and the ΔMosec22 mutant also exhibited defects in mycelial growth, conidial production, and infection of the host plant. Treatment with oxidative stress inducers indicated a breach in cell wall integrity, and staining and quantification assays suggested abnormal chitin deposition on the lateral walls of hyphae of the ΔMosec22 mutant. Furthermore, hypersensitivity to the oxidative stress correlates with the reduced expression of the extracellular enzymes peroxidases and laccases. Our study thus provides new evidence on the conserved function of Sec22 among fungal organisms and indicates that MoSec22 has a role in maintaining cell wall integrity affecting the growth, morphogenesis, and virulence of M. oryzae.
Highlights
Soluble N-ethylmaleimide-sensitive fusion protein attachment protein receptor (SNARE) proteins have been implicated as the conserved core protein machinery for intracellular membrane fusion events of eukaryotic cells including those of fungal organisms [1]
A high of 83% amino acid sequence identity was found to an uncharacterised hypothetical protein from Chaetomium globosum (CHGG07772), and the best match to an annotated Sec22 protein was that of Neurospora crassa (P78746; 79% identity in amino acid sequence)
Further analysis of MoSec22 using the C-terminal SNARE motif revealed that the central position (0-layer) of the heptad repeats of the SNARE motif is an Arg residue, indicating that MoSec22 belongs to the R-SNARE superfamily
Summary
Soluble N-ethylmaleimide-sensitive fusion protein attachment protein receptor (SNARE) proteins have been implicated as the conserved core protein machinery for intracellular membrane fusion events of eukaryotic cells including those of fungal organisms [1]. SNAREs are structurally characterised by a conserved segment of 60–70 amino acids, termed the SNARE motif, a cytoplasmically oriented N-terminal sequence, and a single transmembrane (TM) domain or lipid modification motif at the C-terminus [2,3,4]. Complementary SNAREs characterised by the ‘‘SNARE motif’’ are present on the donor and acceptor membranes prior to fusion, with conserved sequence features and a propensity to form coiled-coils configurations. When efficient member fusion occurs, four SNARE motifs bundle together forming a parallel a-helical coil. This transSNARE complex is referred to as a SNAREpin, and the formation of a SNAREpin pulls the vesicle and target membrane together and may provide the energy to drive fusion of the lipid bilayers [1,5,6,7]. Depending on sequence homology and the presence of an arginine or glutamine residue at the ‘‘0’’ layer of the SNARE motif, SNAREs can be categorised as R- or Qa-, Qb- and Qc-SNAREs [3]
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