Abstract
Mitogen-activated protein kinases (MAPKs) have been demonstrated to be involved in fungal development, sexual reproduction, pathogenicity and/or virulence in many filamentous plant pathogenic fungi, but genes for MAPKs in the fungal cereal pathogen Bipolaris sorokiniana have not been characterized. In this study, orthologues of three MAPK genes (CsSLT2, CsHOG1 and CsFUS3) and one MAPK kinase kinase (MAPKKK) gene (CsSTE11) were identified in the whole genome sequence of the B. sorokiniana isolate ND90Pr, and knockout mutants were generated for each of them. The ∆Csfus3 and ∆Csste11 mutants were defective in conidiation and formation of appressoria-like structures, showed hypersensitivity to oxidative stress and lost pathogenicity on non-wounded leaves of barley cv. Bowman. When inoculated on wounded leaves of Bowman, the ∆Csfus3 and ∆Csste11 mutants were reduced in virulence compared to the wild type. No morphological changes were observed in the ∆Cshog1 mutants in comparison with the wild type; however, they were slightly reduced in growth under oxidative stress and were hypersensitive to hyperosmotic stress. The ∆Cshog1 mutants formed normal appressoria-like structures but were reduced in virulence when inoculated on Bowman leaves. The ∆Csslt2 mutants produced more vegetative hyphae, had lighter pigmentation, were more sensitive to cell wall degrading enzymes, and were reduced in virulence on Bowman leaves, although they formed normal appressoria like the wild type. Root infection assays indicated that the ∆Cshog1 and ∆Csslt2 mutants were able to infect barley roots while the ∆Csfus3 and ∆Csste11 failed to cause any symptoms. However, no significant difference in virulence was observed for ∆Cshog1 mutants while ∆Csslt2 mutants showed significantly reduced virulence on barley roots in comparison with the wild type. Our results indicated that all of these MAPK and MAPKKK genes are involved in the regulation of fungal development under normal and stress conditions and required for full virulence on barley plants.
Highlights
Mitogen-activated protein kinases (MAPKs) have been demonstrated to regulate specialized responses in eukaryotic organisms to environmental signals and molecules from other organisms [1,2,3,4]
Orthologues of these genes were identified in B. sorokiniana, which were designated as CsHOG1, CsSLT2, CsFUS3, and
The predicted protein encoded by the B. sorokiniana CsHOG1 homologue consists of 356 amino acids, which is 99% and 90% identical to the HOG1 in C. heterostrophus (BAD99295.1, NCBI) and OSM1 in M. grisea (AAF09475.1, NCBI), respectively
Summary
Mitogen-activated protein kinases (MAPKs) have been demonstrated to regulate specialized responses in eukaryotic organisms to environmental signals and molecules from other organisms [1,2,3,4]. In S. cerevisiae, the pheromone response pathway is well characterized, where the mating process is regulated by the Ste11-Ste7-Fus3/Kss cascade Several elements of this pathway are found to be involved in filamentous growth of fungi [2]. The first class of MAPKs is represented in Magnaporthe grisea by PMK1 (Pathogenicity MAP Kinase 1), which is orthologous to FUS3/KSS1 of S. cerevisiae [1, 7] This MAPK is required for formation of appressoria and infectious hyphae [1, 7]. The Δmps mutants of C. heterostrophus form normallooking appressoria and are able to penetrate plant cells they are reduced in virulence compared to the wild type [3]. Chste (an ortholog of STE11 in S. cerevisiae) was found to be essential for sexual or asexual development, appressorial formation and pathogenicity in C. heterostrophus [6]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
