Mechanistic insights into the role of Ca2+-stimulated AMPK in the secretion of cellulases during carbon stress

Abstract

AbstractThe response of filamentous fungi towards recalcitrant carbohydrates is majorly governed by transcriptional activators of cellulase genes; however, little is known about the downstream events beyond transcription. We show here inPenicillium funiculosumthat increasing the expression of a transcriptional activator CLR-2 in the catabolically derepressed strain, ΔMig1, didn’t exhibit a synergistic effect on cellulase production unless Ca2+was simultaneously increased. The RNA-seq screen for Ca2+-activated kinases identified SNF1-AMPK and SSP1-AMPKK as being specific to cellulose induction. Deletion ofsnf1led to negligible secretion of cellulase upon induction. Quantitative whole-cell proteomics followed by chemical-genetic experiments withsnf1-deleted strain showed that Ca2+-signaling channelizes carbon, nitrogen and energy sources towards cellulase production. Further, Ca2+-signaling phosphorylates SNF1-AMPK via SSP1, which in turn downregulates the phospho-HOG1 levels, leading to stimulus for cellulase secretion during carbon stress. The findings reported here are significant for understanding fungal pathology and developing second-generation biorefineries.