Fig. 2

Summary of mechanisms and hypotheses for IME169 (reference strain) and IMZ351 (Δmep). For both strains, the main reactions of nitrogen incooperation are GS-GOGAT, Gdh1, Gdh2 and Gdh3, fueling amino acids and biomass synthesis, esp. protein (1) and nucleotides (5). The NH4 transporter proteins Mep1 and Mep2 work as transceptors (6), signaling the presence of ammonium and activate a yet unidentified signaling cascade [57], possibly protein kinase A (PKA) as described in previous works [54, 57]. In the absence of MEP-proteins there is a constitutive down-regulation/repression of PKA and up-regulation/activation of genes associated with autophagy and DNA replication stress (see main text). These stress responses lead to decreased DNA replication and protein biosynthesis and increased protein turnover (3). The protein turnover could result in production of amino acids and/or higher NHX concentrations (4), amino acid recycling and trehalose overproduction