Characterization of GAPDH expression related to biotic stress responses in Physcomitrella

Glyceraldehyde 3-phosphate dehydrogenase (GAPDH) is a housekeeping protein that plays an important role in the energy metabolism and is found in all kingdoms of life. While animals possess one GAPDH isoform, plants possess several GAPDHs. GAPA and GAPB are chloroplastic phosphorylating GAPDHs involved in the Calvin-Benson cycle. GAPC in the cytosol and GAPCp in plastids are glycolytic phosphorylating GAPDHs involved in the glycolysis pathway. In animals as well as in plants, GAPDH isoforms have various non-metabolic roles, e.g. in autophagy, apoptosis, and were identified as redox sensors. In plants, in addition to the variety of moonlight functions in abiotic stress, GAPDHs are also involved in biotic stress responses. Here, we identified 17 GAPDH isoforms from the moss Physcomitrella, belonging to the GAPA, GAPC, and GAPCp. We searched for protein and transcript evidences in publicly available proteome and transcriptome data, laying the focus on datasets of treatments with the phytohormones salicylic acid (SA) and methyl jasmonate (MeJA). We investigated the putative role of GAPDHs in plant immune response by identifying SA- and MeJA-inducible GAPAs and GAPC genes. The GAPAs Pp3c1_13170 and Pp3c11_15790 and the GAPC Pp3c18_15450 appear to be unresponsive to SA treatment. In contrast, we identified four MeJA-responsive genes. MeJA-treatment resulted in a 10- and 3-fold downregulation of the GAPAs Pp3c1_13170 and Pp3c11_15790, whereas expression of the two GAPC genes Pp3c18_15450 and Pp3c21_9380 showed an up to 7- and 33-fold upregulation after 4 hours of MeJA treatment, respectively. Simultaneously, a four-hour MeJA-treatment induced the remodeling of the Physcomitrella secretome, resulting in the production of antimicrobial compounds, which in turn led to a bacteriostatic growth inhibition of 26% of E. coli. These findings draw attention to the potential differential regulation of GAPDH genes in plant immune response as well as a potential role for GAPC in the defense response against necrotrophic pathogens.