BcSAK1, a Stress-Activated Mitogen-Activated Protein Kinase, Is Involved in Vegetative Differentiation and Pathogenicity in Botrytis cinerea

Abstract

The gene bcsak1, encoding a mitogen-activated protein kinase (MAPK) of Botrytis cinerea, was cloned and characterized. The protein has high homology to the yeast Hog1 and to corresponding MAPKs from filamentous fungi, but it shows unique functional features. The protein is phosphorylated under osmotic stress, specific fungicides, and oxidative stress mediated by H 2 O 2 and menadione. Northern blot analyses indicate that only a subset of typical oxidative stress response genes is regulated by BcSAK1. In contrast to most other fungal systems, ⌬bcsak1 mutants are significantly impaired in vegetative and pathogenic development: they are blocked in conidia formation, show increased sclerotial development, and are unable to penetrate unwounded plant tissue. These data indicate that in B. cinerea the stress-activated MAPK cascade is involved in essential differentiation programs.

Mitogen-Activated Protein Kinase Signaling in Plant-Interacting Fungi: Distinct Messages from Conserved Messengers

“…On the other hand, deletion of Mgr-Hog1 produces nonpathogenic M. graminicola strains that are impaired in mating and thus unable to switch from a yeast-like form to filamentous growth (Mehrabi et al, 2006b). In B. cinerea, deletion of SAK1 (here renamed Bci-Hog1) also creates nonpathogenic strains that are unable to penetrate unwounded plant tissues (Segmüller et al, 2007). Taken as a whole, these results indicate that Hog1-type MAPKs are required for virulence of some, but not all, plant pathogens.…”

“…For instance, hypersensitivity to osmotic stress is not only reported for the Mor-hog1 mutants (Dixon et al, 1999) but also for mutants of Cryphonectria parasitica, C. orbiculare, B. oryzae, M. graminicola, and B. cinerea lacking their respective Hog1 homologs (Kojima et al, 2004;Park et al, 2004b;Mehrabi et al, 2006b;Moriwaki et al, 2006;Segmüller et al, 2007). In filamentous fungi, reports have also linked the activity of group III His kinases to the phosphorylation status of Hog1-type MAPKs.…”

Two-Component Signaling System in Filamentous Fungi and the Mode of Action of Dicarboximide and Phenylpyrrole Fungicides

“…In B. cinerea, a Group III HisK gene disruptant forms very few conidia (Viaud et al, 2006). This characteristic can also be found in a downstream HOG1 MAPK gene disruptant (Segmüller et al, 2007). In these two disruptants, sclerotia are formed in very large quantities.…”

“…In addition to this role in morphogenesis, the osmotic signaling system of B. cinerea plays a critical role in plant infection. Both the Group III HisK and HOG1 MAPK disruptants are largely non-pathogenic to host plants (Izumitsu et al, 2010;Segmüller et al, 2007;Viaud et al, 2006). The fact that in B. cinerea, the mutations of the fungicide resistance genes interferes with its pathogenicity, and morphogenesis may provide a scientific basis for understanding the well-known fact that there is a loss of fitness associated with dicarboximide resistance, resulting in a decrease in the frequency of resistant strains when dicarboximides are no longer applied (q.v.…”

The Mitogen-Activated Protein Kinase Signal Transduction Pathways in Alternaria Species

“…Three MAPK signaling pathways named as pmk1, mps1 and osm1 play diverse roles in pathogenesis-related development (Dixon et al, 1999;Xu and Hamer, 1996;Xu et al, 1998). Other plant pathogens, e.g., Colletotrichum lagenarium (Kojima et al, 2002;Kojima et al, 2004;Takano et al, 2000), Botrytis cinerea Rui and Hahn, 2007;Segmuller et al, 2006) and Mycosphaerella graminicola (Cousin et al, 2006;Mehrabi et al, 2006a;Moriwaki et al, 2006) have also been studied in depth on the functions of their MAPK signaling pathways.…”