Disruption of a phytochrome-like histidine kinase gene by homologous recombination leads to a significant reduction in vegetative growth, sclerotia production, and the pathogenicity of Botrytis cinerea

• A histidine kinase gene disruption mutant ΔBcphy3-P21 was obtained in B. cinerea.
• The mutant strain ΔBcphy3-P21 lost the ability to produce sclerotia.
• The ΔBcphy3-P21 displayed reduced pathogenicity on different tested plant tissues.
• The chitin content of cell wall was reduced in mutant strain ΔBcphy3-P21.

Phytochrome-like histidine kinases are photoreceptors that help a wide variety of bacteria and fungi perceive environmental light. In this study, a putative histidine kinase gene Bcphy3 from Botrytis cinerea was disrupted, and a Bcphy3 mutant ΔBcphy3-P21 was obtained. This mutant formed smaller colonies on PDA media compared to the wild-type strain Bc05.10 (approximately 70% of Bc05.10), indicating that the absence of Bcphy3 affected the growth rate of ΔBcphy3-P21. The mutant also produced a substantially reduced amount of sclerotia compared to Bc05.10. Moreover, the ΔBcphy3-P21 strain displayed significantly reduced pathogenicity on different tested plant tissues (capsicum, lettuce, tomato, grape berry, and carrot). Further phenotypic analysis showed that the ΔBcphy3-P21 mutant was more susceptible to cell wall stress caused by Congo red, suggesting that the absence of Bcphy3 may also affect cell wall integrity. Transmission electron microscopy analysis further confirmed that the layer of cell wall mainly composed of chitin was much thinner, and the outer layer of cell wall was disorganized in ΔBcphy3-P21. Gene transcription analysis demonstrated that the expression of the chitin synthesis genes (Bcchs1 and Bcchs3a) was inhibited in ΔBcphy3-P21. Determination of the chitin content revealed that the chitin content of the mycelium in the ΔBcphy3 mutant was reduced by approximately 19% compared to the wild-type strain Bc05.10. Taken together, our results indicated that Bcphy3 encoding a histidine kinase is required for normal vegetative growth, scler