The Group III Two-Component Histidine Kinase of Filamentous Fungi Is Involved in the Fungicidal Activity of the Bacterial Polyketide Ambruticin

Abstract

We have shown that the plant pathogen Alternaria brassicicola exhibited very high susceptibility to ambruticin VS4 and to a lesser extent to the phenylpyrrole fungicide fludioxonil. These compounds are both derived from natural bacterial metabolites with antifungal properties and are thought to exert their toxicity by interfering with osmoregulation in filamentous fungi. Disruption of the osmosensor group III histidine kinase gene AbNIK1 (for A. brassicola NIK1) resulted in high levels of resistance to ambruticin and fludioxonil, while a mutant isolate characterized by a single-amino-acid substitution in the HAMP domain of the kinase only exhibited moderate resistance. Moreover, the natural resistance of Saccharomyces cerevisiae to these antifungal molecules switched to sensitivity in strains expressing AbNIK1p. We also showed that exposure to fludioxonil and ambruticin resulted in abnormal phosphorylation of a Hog1-like mitogen-activated protein kinase (MAPK) in A. brassicicola. Parallel experiments carried out with wild-type and mutant isolates of Neurospora crassa revealed that, in this species, ambruticin susceptibility was dependent on the OS1-RRG1 branch of the phosphorelay pathway downstream of the OS2 MAPK cascade but independent of the yeast Skn7-like response regulator RRG2. These results show that the ability to synthesize a functional group III histidine kinase is a prerequisite for the expression of ambruticin and phenylpyrrole susceptibility in A. brassicicola and N. crassa and that, at least in the latter species, improper activation of the high-osmolarity glycerol-related pathway could explain their fungicidal properties.

Characterization of NikA Histidine Kinase and Two Response Regulators with Special Reference to Osmotic Adaptation and Asexual Development inAspergillus nidulans

“…[17][18][19]21) In this regard, we have proposed a model of the NikA-SskA/SrrA phosphorelay system, responsible for the response to these fungicides in A. nidulans. 12) To explain some of the new results from this study, we used this model ( 12)…”

“…Those NikA orthologs are Nik1/ Os-1 (Neurospora crassa), 6,16) Hik1 (Magnaporthe grisea), 17) Bos1 (Botrytis cinerea), 18) Dic1 (Cochliobolus heterostrophus), 19) and AbNik1 (Alternaria brassicicola). 20,21) The C. heterostrophus RRs, ChSsk1 and ChSkn7 (SrrA ortholog), have also been reported to be responsible for the growth-inhibitory effects of fungicides. 22) Hence, the HK-RR (NikA-SskA/SrrA) system, in which NikA-HK phosphorylates the RRs SskA and SrrA, with YpdA as the intermediate, appears to play a crucial role in the fungicide response among filamentous fungi.…”

The Genomes of Three Uneven Siblings: Footprints of the Lifestyles of Three Trichoderma Species

“…They are composed of hybrid sensor kinases, a histidine phosphotransferase (HPt), and response regulators. They sense and transmit signals from the environment and subsequently activate, for example, the HOG1/osmolarity and stress-sensing pathway (728,729). Hence, the MAPKKKs TR_57513, TA_295042, and TV_195699 are likely targets of the two-component phosphorelay system.…”

Mitogen-activated protein kinase signaling pathways of the tangerine pathotype of Alternaria alternata

“…Graminicola, C. heterostrophus and F. graminearum. [76][77][78][79][80][81][82][83][84][85][86][87][88][89] The A. alternata Hog1 (AaHog1), analogous to the yeast Hog1, has a distinct phosphorylation motif (TGY) required for the hyperosmolarity response. 5 AaHog1 also has a protein kinase ATP-binding region, a MAP kinase and a serine/threonine protein kinase active site.…”