Regulation of fungal raw-starch-degrading enzyme production depends on transcription factor phosphorylation and recruitment of the Mediator complex

Abstract

Filamentous fungus can produce raw-starch-degrading enzyme (RSDE) that efficiently degrades raw starch below starch gelatinization temperature. Employment of RSDE in starch processing can save energy. A key putative transcription factor PoxRsrA (production of raw-starch-degrading enzyme regulation in Penicilliumoxalicum) was identified to regulate RSDE production in P. oxalicum; however, its regulatory mechanism remains unclear. Here we show that PoxRsrA1434–1730 was the transcriptional activation domain, with essential residues, D1508, W1509 and M1510. SANT (SWI3, ADA2, N-CoR and TFIIIB)-like domain 1 (SANT1) bound to DNA at the sequence 5′-RHCDDGGD-3′ in the promoter regions of genes encoding major amylases, with an essential residue, R866. SANT2 interacted with a putative 3-hydroxyisobutyryl-CoA hydrolase, which suppressed phosphorylation at tyrosines Y1127 and Y1170 of PoxRsrA901–1360, thereby inhibiting RSDE biosynthesis. PoxRsrA1135–1439 regulated mycelial sporulation by interacting with Mediator subunit Med6, whereas PoxRsrA1440–1794 regulated RSDE biosynthesis by binding to Med31. Overexpression of PoxRsrA increased sporulation and RSDE production. These findings provide insights into the regulatory mechanisms of fungal RSDE biosynthesis.