Laccaria bicolor adapts to phosphate deficiency at the developmental, metabolic and gene expression levels

This study aimed to decipher how the free-living ECM Laccaria bicolor adapts to Pi deficiency. L. bicolor mycelium grown for 7 days in medium without Pi showed very low Pi and polyphosphate reserves and grew in less compact but larger colonies. Pi deficiency resulted in approximately 1500-2000 genes being up- and down-regulated more than 2-fold compared to the mycelium grown with abundant Pi, with most genes partially reverting their expression pattern in cultures spiked with Pi for 24 hours. Numerous genes involved in Pi mobilization from organic sources, such as phosphatases and ribonucleases, were induced by Pi deficiency, as well as genes involved in Pi transport, and such expression patterns were matched by increase enzymatic activities. Pi deficiency also induced the synthesis of the betaine lipid diacylglyceryl-N,N,N-trimethylhomoserine (DGTS). Several genes induced by mycorrhization, such as those encoding protease inhibitors belonging to the mycocytin family and Micorrhizae-Induced Small Secreted Peptides (MiSSP), were also induced by Pi deficiency. Overall design: Dikaryotic strain L. bicolor S238N was grown in liquid P5 medium with 7 mM inorganic phosphate (HP samples) or without phosphate (LP samples) for 7days. One set of cultures grown without phosphate for 7 day was spiked with 7 mM phosphate and grown for one additional day (LPspike sample). For each set, three independent replicates were generated and analyzed by RNAseq.