Production of reactive oxygen species ROS at the

Production of reactive oxygen species (ROS) at the site of pathogen attack following recognition of pathogen-associated molecular patterns (PAMPs) is regarded as one of the initial plant immune responses. ROS accumulation can induce a hypersensitive reaction in host plants, thereby causing programmed cell death and cellular defense against pathogen invasion [21], [22]. NbrbohA and NbrbohB virus-induced gene silencing in Nicotiana benthamiana plants has been shown to reduce ROS accumulation at the infection site and decrease resistance to P. infestans[23]. Similarly, ROS triggered by human polymorphonuclear neutrophils is considered to be the main mechanism for defense against the human pathogen C. neoformans[24]. These results further demonstrate that host-derived ROS is important in counteracting pathogen invasion during the plant–microbe interaction. In response to these defenses and to successfully invade a host, plant pathogens have developed strategies to detoxify host-derived ROS at the site of infection. Deletion of the yap1 gene (a homolog of transcription factor AP-1 from S. cerevisiae) in Ustilago maydis caused higher sensitivity to H2O2 than did wild type antifungal and it significantly reduced virulence [25]. In Claviceps purpurea, deletion of transcriptional factor CPTF1 increases H2O2 accumulation at the invasion site following the defense reaction to pathogen attack [26]. Magnaporthe oryzae gene des1, affecting the expression of related peroxidase and laccase coding genes, is involved in detoxifying ROS at the initial infection site, and des1deletion mutants lose pathogenicity in rice [27]. In M. oryzae, deletion of Moatf1, a homolog of basic leucine zipper (bZIP) transcription factor ATF/CREB in S. pombe regulating the oxidative stress response, caused retarded vegetative growth of mycelia and exhibited higher sensitivity to H2O2, thereby leading to significantly reduced virulence in rice cv. CO-39 [28]. These results further demonstrate that avoiding ROS-mediated host defenses is key for phytopathogens to successfully invade their hosts. Thus, research on mechanisms of how phytopathogens detoxify host-derived ROS at the infection site could help to elucidate the molecular basis of pathogenicity in plant–microbe interactions. In this work, a gene, PsGcn5, was identified in P. sojae as a homolog of one component of the widely occurring SAGA complex. Multiple alignment analyses showed a conserved histone acetyltransferase domain and a conserved bromodomain. PsGcn5 was found to be important in growth under conditions of oxidative stress and to contribute to the full virulence of P. sojae by suppressing the host-derived ROS.
Materials and methods
Results
Discussion The histone acetyltransferases Gcn5 is moderately well conserved across different species, but its biological functions are not well characterized in filamentous phytopathogens, particularly in Phytophthora spp. In this study, we functionally characterized the P. sojae histone acetyltransferase protein (PsGcn5). PsGcn5 is conserved in the oomycete genome, and contains a histone acetyltransferase domain and a bromodomain PsGcn5 was responsible for the regulation of oxidative stress tolerance and was required for pathogenicity in P. sojae. In many organisms, each element of the SAGA complex is essential in multi-protein chromatin remodeling complexes. Except for acetylating core histones, the SAGA complex performs multiple functions including recruiting the pre-initiation complex, and deubiquitinating monoubiquitinated histone [37]. The majority putative homologs of the yeast SAGA complex have been found in the P. sojae genome, with two exceptions: Spt20 and Sgf73, which are essential for the structural integrity of the SAGA complex and preinitiation SAGA complex assembly at promoters in S. cerevisiae respectively [6], were not readily identifiable by sequence homology. Of the genes present, the P. sojae PsGcn5 gene has been shown to be the most sequence identity, which shares 68% acetyltransferase and 31% bromodomains identity with the homologs of S. cerevisiae, respectively.