Thioredoxins are involved in the activation of the PMK1 MAP kinase pathway during appressorium penetration and invasive growth in Magnaporthe oryzae

Abstract

In Magnaporthe oryzae, the Mst11-Mst7-Pmk1 MAP kinase pathway is essential for appressorium formation and invasive growth. To determine their roles in Pmk1 activation and plant infection, we characterized the two thioredoxin genes, TRX1 and TRX2, in M. oryzae. Whereas the Δtrx1 mutants had no detectable phenotypes, deletion of TRX2 caused pleiotropic defects in growth, conidiation, light sensing, responses to stresses and plant infection progresses. The Δtrx1 Δtrx2 double mutant had more severe defects than the Δtrx2 mutant and was non-pathogenic in infection assays. The Δtrx2 and Δtrx1 Δtrx2 mutant rarely formed appressoria on hyphal tips and were defective in invasive growth after penetration. Pmk1 phosphorylation was barely detectable in the Δtrx2 and Δtrx1 Δtrx2 mutants. Deletion of TRX2 affected proper folding or intra-/inter-molecular interaction of Mst7 and expression of the dominant active MST7 allele partially rescued the defects of the Δtrx1 Δtrx2 mutant. Furthermore, Cys305 is important for Mst7 function and Trx2 directly interacts with Mst7 in co-IP assays. Our data indicated that thioredoxins play important roles in intra-cellular ROS signalling and pathogenesis in M. oryzae. As the predominant thioredoxin gene, TRX2 may regulate the activation of Pmk1 MAPK via its effects on Mst7.

The thioredoxin MoTrx2 protein mediates reactive oxygen species (ROS) balance and controls pathogenicity as a target of the transcription factor MoAP1 in Magnaporthe oryzae

“…S4A, see Supporting Information), similar to that reported by Zhang et al . (). To examine the role of MoTrx2 in sexual reproduction, the wild‐type, ΔMotrx2 mutants and complemented strains ( MAT1‐2 ) were tested in confrontation with the standard test strain TH3 ( MAT1‐1 ).…”

“…S5B). These findings are again in accordance with those described by Zhang and colleagues (Zhang et al ., ), suggesting that the attenuated virulence of ΔMotrx2 mutants is caused by a defect in infectious hyphal growth.…”

“…A recent study has found that there are two thioredoxins, MoTrx1 and MoTrx2, in M. oryzae , and that MoTrx2 interacts with MoMst7 of the PMK1 mitogen‐activated protein (MAP) kinase pathway to control appressorium function and infection (Zhang et al ., ). Here, we provide evidence to show how MoTrx2 may exert its function through regulation by the transcription factor MoAP1.…”

Reactive oxygen species metabolism and plant-fungal interactions

“…The thioredoxin system contains thioredoxins (Trx), and the NADPH-dependent enzyme thioredoxin reductase (TrxR) (Lu and Holmgren, 2014;Fernandez and Wilson, 2014). Thioredoxins are ubiquitous redox proteins containing cysteine residues that are reversibly redox active, cycling between oxidized disulfide (Trx-S 2 ) and reduced dithiol [Trx-(SH) 2 ] in a TrxR dependent manner (Holmgren, 1989;Zhang et al, 2016). Small ubiquitous glutaredoxin proteins, part of the glutathione system, are also required for ROS scavenging.…”

“…Additionally, the thioredoxin and glutathione antioxidation systems play a crucial role in pathogenicity. Thioredoxin peroxidase (Tpx1), thioredoxin reductase (Trr1) and the thioredoxin Trx2 (but not Trx1), are required for in planta proliferation and intracellular ROS metabolism, but not for overcoming plantderived ROS Zhang et al, 2016). Glutathione reductase (Gtr1) is required for both in planta proliferation of M. oryzae and neutralizing host-derived ROS accumulation .…”