S. Ying

Convergent roles of six fungal specific transcription factors in insecticidal process and environmental fitness of Beauveria bassiana.

BACKGROUND A family of 54 fungal specific transcription factors (FsTFs) with the FsTF domain fungal_TF_MHR or fungal_trans_2 coexist with a large class of 202 C6 transcription factors (TFs) with Zn(II)2Cys6 binuclear cluster DNA-binding (C6) domain alone or both C6 and FsTF domains in Beauveria bassiana, a wide-spectrum mycoinsecticide. FsTFs and C6 TFs are often confused with each other and are generally underexplored, making it necessary to explore their regulatory roles in the fungal insect-pathogenic lifecycle. Here, six FsTFs (TF1-TF6) with different (representative) molecular sizes and unique size-different FsTF domain located in different sequence regions are functionally characterized. RESULTS The deletion mutants of tf1-tf6 were much more compromised in virulence via normal cuticle infection (NCI) than cuticle-bypassing infection (intrahemocoel injection). The markedly attenuated virulence via NCI was ascribed to severely blocked secretion of cuticle-degrading enzymes required for hyphal invasion into host hemocoel through cuticular penetration. All the mutants also exhibited increased sensitivities to hyperosmotic, oxidative and cell wall perturbing stresses, impaired conidial quality, and sharp increases in submerged blastospore production in vitro despite negligible changes in aerial conidiation and radial growth on different carbon or nitrogen sources. The altered phenotypes were well restored by targeted gene complementation. CONCLUSION TF1-TF6 play essential roles in the positive regulation of insect-pathogenic lifecycle and serve as negative regulators of submerged blastospore production in vitro in B. bassiana. These findings add knowledge to the family of FsTFs and unveil convergent evolution of TF1-TF6 in supporting the insecticidal activity and environmental fitness of B. bassiana. © 2026 Society of Chemical Industry.

Bbsmf1, an Nramp Family Transporter, Sustains Iron Homeostasis Through Cross Pathway Compensation in Beauveria bassiana

Differential roles of three subclass III C6 transcription factors in the insect-pathogenic lifecycle of Beauveria bassiana.

Six subclass III C6 transcription factors (TFs) with unique Zn(II)2Cys6 binuclear cluster DNA-binding (C6 or GAL4) domain not locating at N-terminus are underexplored in Beauveria bassiana, a wide-spectrum mycoinsecticide. Here, we report that three C6 TFs with the GAL4 domain locating at C-terminus (TF1), between C-terminal and central regions (TF2) and between central and N-terminal regions (TF3) are largely differentiated in function. TF1 was proven to localize in both nucleus and cytoplasm and regulate host immune repression in the course of host hemocoel colonization instead of cuticular penetration. The deletion of tf1 resulted in much greater virulence loss via normal cuticle infection (77%) than cuticle-bypassing infection (25%) for direct hemocoel colonization by intrahemocoel injection. The deletion also led to severe defects in radial growth, multiple stress tolerances, aerial conidiation, and submerged blastospore production as well as resistance to host immune defense after invasion into host hemocoel, unveiling pleiotropic effects of TF1 in the fungal lifecycle. TF3 was similar to TF1 in subcellular feature and exhibited lesser role than TF1 in mediating conidiation and blastospore production but no other role. TF2 looks like a typical subclass III C6 TF but proved functionally null perhaps due to its localization in neither nucleus nor cytoplasm under normal culture conditions. These findings add knowledge to subclass III C6 TFs and unveil a significance of host immune suppression for the insecticidal activity of B. bassiana after hyphal invasion into insect hemocoel through cuticular penetration.