BcIqg1, a fungal IQGAP homolog, interacts with NADPH oxidase, MAP kinase and calcium signaling proteins and regulates virulence and development in Botrytis cinerea

Abstract

NADPH oxidases (Nox) produce reactive oxygen species (ROS) in multicellular eukaryotic organisms. They trigger defense reactions ('oxidative burst') - in phagocytes and plant cells -, and are involved in a broad range of differentiation processes. Fungal Nox-complexes play a central role in vegetative, sexual and pathogenic processes. In contrast to mammalian systems, knowledge is limited about composition, localisation and connection to major signaling cascades in fungi. Here, we characterize a fungal homolog of the RasGAP scaffold protein IQGAP, which links several major signaling processes, including Nox in mammalian cell lines. We show that BcIqg1 interacts directly with a cytosolic, regulatory component (BcRac) and a membrane-associated subunit (BcNoxD) of a Nox-complex in the pathogen Botrytis cinerea. Thus, this protein may be a scaffold that mediates interaction of the catalytic subunits with the regulator BcNoxR. The protein interacts with modules of the MAP kinase- and calcium-dependent signaling pathways. Functional analysis of BcIqg1 substantiated its involvement in different signaling pathways. It mediates the Ca(2+) -triggered nuclear translocation of - BcCRZ1 and the MAP kinase BcBmp1. BcIqg1 is involved in resistance against oxidative and membrane stress and is required for several developmental processes including formation of sclerotia, conidial anastomosis tubes and infection cushions as well as for virulence.

The septin protein Sep4 facilitates host infection by plant fungal pathogens via mediating initiation of infection structure formation

“…NAD(P)H oxidases (Nox) are the major ROS producing enzymes and fungal Nox‐complexes play a central role in vegetative and pathogenic processes (Marschall and Tudzynski, ). In M. oryzae , ROS generation is required for both F‐actin and septin ring assembly around the appressorium pore, where the penetration peg emerges to rupture the leaf cuticle (Ryder et al ., ).…”

“…Infection structures (IFSs), mainly including appressoria and infection cushions (ICs), play crucial roles in many phytopathogenic fungi by mediating host penetration (Dagdas et al ., ; Ryder et al ., ; Marschall and Tudzynski, ). After germination of conidia and a short period of vegetative growth, the germling tubes cease their polarized cell growth and start to form swelled and melanized IFSs called appressoria.…”

Reactive oxygen species metabolism and plant-fungal interactions

“…In M. oryzae, NOXD gene expression is dependent on a Zn(II) 2 Cys 6 family transcription factor that also interacts with machinery of the Map kinase signaling cascade (Galhano et al, 2017). In B. cinerea, the RasGAP protein homolog IQGAP interacts with NoxA, has a role in oxidative stress, and connects ROS signaling with MAP kinase and calcium signaling cascades (Marschall and Tudzynski, 2016c). Because the NoxD adapter protein only interacts with NoxA (Fig.…”

The Protein Disulfide Isomerase of Botrytis cinerea: An ER Protein Involved in Protein Folding and Redox Homeostasis Influences NADPH Oxidase Signaling Processes

“…However, despite the evolutionary distance, there are several homologies between mammalian and fungal Nox complexes. For example, homologs in B. cinerea were identified for the catalytic subunit (gp91phox – BcNoxA/B), the regulatory subunit (p67phox – BcNoxR), adaptor proteins (p22phox – BcNoxD) as well as for putative transient members of Nox complexes such as the scaffold protein IQGAP (BcIqg1) (Segmueller et al, 2008; Siegmund et al, 2013, 2015; Marschall and Tudzynski, 2016a). Additionally, mammalian and fungal Nox complexes were shown to have functions in different cellular compartments with a changing complex composition dependent on the respective developmental process (reviewed in Laurindo et al, 2014; Marschall and Tudzynski, 2016b; Marschall et al, 2016a).…”

“…Since analyses in plants reveal a tight and recurrent connection between ROS and Ca 2+ signaling pathways (Steinhorst and Kudla, 2014) many studies aim to unravel putative signaling hubs in fungi. Most recently, we were able to show that the protein BcIqg1 interacts with members of ROS and Ca 2+ signaling cascades, though it remained unresolved whether the protein contributes to both pathways at the same time or independently (Marschall and Tudzynski, 2016a). Apart from the latter aspects, we have also unraveled the connection between both signaling pathways and the level of redox-mediated processes.…”