A two‐component histidine kinase S hk1 controls stress response, sclerotial formation and fungicide resistance in S clerotinia sclerotiorum

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Abstract
Summary: Fungal histidine kinases ( HKs ) are involved in osmotic and oxidative stress responses, hyphal development, fungicide sensitivity and virulence. Members of HK class III are known to signal through the high‐osmolarity glycerol mitogen‐activated protein kinase ( HOG MAPK ). In this study, we characterized the S hk1 gene ( SS1G _12694.3), which encodes a putative class III HK , from the plant pathogen S clerotinia sclerotiorum . Disruption of S hk1 resulted in resistance to phenylpyrrole and dicarboximide fungicides and increased sensitivity to hyperosmotic stress and H 2 O 2 ‐induced oxidative stress. The S hk1 mutant showed a significant reduction in vegetative hyphal growth and was unable to produce sclerotia. Quantitative real‐time polymerase chain reaction ( qRT‐PCR and glycerol determination assays showed that the expression of SsHOG1 (the last kinase of the H og pathway) and glycerol accumulation were regulated by the S hk1 gene, but PAK (p21‐activated kinase) was not. In addition, the S hk1 mutant showed no change in virulence. All the defects were restored by genetic complementation of the S hk1 deletion mutant with the wild‐type S hk1 gene. These findings indicate that S hk1 is involved in vegetative differentiation, sclerotial formation, glycerol accumulation and adaption to hyperosmotic and oxidative stresses, and to fungicides, in S . sclerotiorum . Taken together, our results demonstrate, for the first time, the role of two‐component HKs in S clerotinia .

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