MADS-box transcriptional regulation of dimorphic transition in Penicillium marneffei
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Systemic dimorphic fungi collectively cause over one million new infections every year. Latent infectionsworldwide grow to the tens of millions, making them a priority for today''s research. Penicillium marneffei (Pm)is of particular concern due to a marked increase in the number of cases of penicilliosis in the last 20 years,which has been concurrent with the rise in immunosuppression due to the global spread of HIV infections. Pmgrows as hypha in its environmental reservoir and as yeast in mammalian hosts. The phase transition betweenthe two growth forms is considered to be essential for its pathogenicity and the transmission of penicilliosis.The transition between hypha and yeast is reversible and can be triggered at a sharp threshold temperature of37Â°C. The precise mechanisms underlying the thermosensing and the phase transition in Pm remain unknown.Therefore, there is a critical need to identify key genes and regulatory processes involved in the morphogeneticcontrol in Pm. The applicants'' recent findings provide a promising, new opportunity for target identification.Using an innovative, serial culture-based experimental evolution (EE) technique, the applicants derived mutantPm strains that undergo the hypha-to-yeast phase transition at 30Â°C rather than 37Â°C. DNA- and RNA-sequencing of the mutant and wild-type strains revealed important roles of a family of MADS-box transcriptionfactor (TF) genes, especially madsB and madsA, in regulating thermal dimorphism in Pm. The expression ofmadsB in wild type is up-regulated 1,500-fold during the hypha-to-yeast transition. The madsB loss-of-functionmutation caused by genomic deletion in mutant strains seems to be responsible for the lower thresholdtemperature of phase transition. Significantly, EE-derived mutants are found to be completely avirulent in themouse model, suggesting that the precise threshold temperature at 37Â°C for the phase transition is essentialfor Pm to infect and/or adapt to the host condition. Furthermore, the overexpression of madsA causes Pm togrow as hypha instead of yeast at 37Â°C. These preliminary data led to the central hypothesis that the Pmthermosensing systems act through temperature-responsive activities of the MADS-box TFs. Based on thesepreliminary results, the applicants propose the following two Specific Aims: (1) determine the roles of madsBand madsA in regulating thermal dimorphism in Pm, and (2) identify the downstream targets of MadsB andMadsA. Upon completion of the proposed research, the applicants expect to critically test the functions of thetwo MADS-box TFs in regulating dimorphic development in Pm (Aim 1). The applicants will identify thedownstream targets of MadsB and/or MadsA, and examine the functions of selected targets in Pm (Aim 2).Together, these results will provide much-needed entry points to further investigate the otherwise mysteriousmechanisms underlying thermal dimorphism in this important but understudied fungal pathogen.