Roles of Protein Kinase A and Adenylate Cyclase in Light-Modulated Cellulase Regulation in Trichoderma reesei

Abstract

<jats:title>ABSTRACT</jats:title><jats:p>The cyclic AMP (cAMP) pathway represents a central signaling cascade with crucial functions in all organisms. Previous studies of<jats:named-content content-type="genus-species">Trichoderma reesei</jats:named-content>(anamorph of<jats:named-content content-type="genus-species">Hypocrea jecorina</jats:named-content>) suggested a function of cAMP signaling in regulation of cellulase gene expression. We were therefore interested in how the crucial components of this pathway, adenylate cyclase (ACY1) and cAMP-dependent protein kinase A (PKA), would affect cellulase gene expression. We found that both ACY1 and PKA catalytic subunit 1 (PKAC1) are involved in regulation of vegetative growth but are not essential for sexual development. Interestingly, our results showed considerably increased transcript abundance of cellulase genes in darkness compared to light (light responsiveness) upon growth on lactose. This effect is strongly enhanced in mutant strains lacking PKAC1 or ACY1. Comparison to the wild type showed that ACY1 has a consistently positive effect on cellulase gene expression in light and darkness, while PKAC1 influences transcript levels of cellulase genes positively in light but negatively in darkness. A function of PKAC1 in light-modulated cellulase gene regulation is also reflected by altered complex formation within the<jats:italic>cel6a/cbh2</jats:italic>promoter in light and darkness and in the absence of<jats:italic>pkac1</jats:italic>. Analysis of transcript levels of cellulase regulator genes indicates that the regulatory output of the cAMP pathway may be established via adjustment of XYR1 abundance. Consequently, both adenylate cyclase and protein kinase A are involved in light-modulated cellulase gene expression in<jats:named-content content-type="genus-species">T. reesei</jats:named-content>and have a dampening effect on the light responsiveness of this process.</jats:p>

The Genomes of Three Uneven Siblings: Footprints of the Lifestyles of Three Trichoderma Species

“…In T. reesei, sexual development is influenced by light response (885) and nutrient-sensing pathways (350,642,891). Analysis of the mating competence of the original isolate of T. reesei, QM6a, revealed that this strain is female sterile, i.e., artificial exchange of the mating type of this strain did not enable sexual development (859).…”

“…PKAc1 (TR_57399, TA_164264, and TV_184045), which is considered the major PKA catalytic subunit, impacts growth and sexual and asexual development, as well as cellulase regulation in T. reesei (642). T. reesei, T. atroviride, and T. virens also encode a second PKA catalytic subunit (PKAc2; TR_65873, TA_52331, and TV_214212), but its function has not been studied so far.…”

“…Mutants of S. cerevisiae lacking either Ras1p or Cdc35p are unviable because both proteins are required for activating cAMP synthesis, which is essential for cells to progress through the G 1 phase of the cell cycle. ACY1 mutants of T. reesei are viable but show a severe growth defect phenotype (642). Ras1p plays an important role in regulating pseudohyphal growth by activating a MAPK cascade and the cAMP/PKA cascade (677).…”

“…With respect to protein kinase A, T. reesei, T. atroviride, and T. virens have one regulatory subunit (PKAr1; TR_75878, TA_29552, and TV_214426) and two cata-lytic subunits (PKAc1, via TR_57399, TA_164264, and TV_184045; PKAc2, via TR_65873, TA_52331, and TV_214212). ACY1 and PKAc1 are involved in regulation of vegetative growth, cellulase gene expression, and development but are not essential for sexual development in T. reesei (642). In T. atroviride, protein kinase A is involved in regulation of conidiation and induction of early light response genes (52).…”

Trichoderma Research in the Genome Era

“…Nutrient deprivation or different nutrient sources are universal signals for conidiation, and light is a determinant for the utilization and/or uptake of specific carbon sources by Trichoderma species (132). Several components of the heterotrimeric G-protein and cAMP pathways and two Ras GTPases impact sporulation, often in a light-and nutrient-dependent manner (103,109,112,115,131,147). Conidiation by T. viride and T. atroviride is strongly carbonsource dependent in light and darkness (21,39).…”