Ariana Casas-Román, María-José Lorite, Juan Sanjuán, María-Trinidad Gallegos

Microbiol Research; 2024 Jan:278: 127530. doi: 10.1016/j.micres.2023.127530. 

Figure: Tomato disease symptom by Pseudomonas syringae pv. tomato.

Abstract

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH or Gap) is a ubiquitously distributed enzyme that plays an essential role in the glycolytic and gluconeogenic pathways. However, additional roles have been described unrelated to its enzymatic function in diverse organisms, often linked to its presence in the cell surface or as a secreted protein. Despite being a paradigm among multifunctional/moonlighting proteins, little is known about its possible roles in phytopathogenic bacteria. In the present work we have studied three putative gap paralogous genes identified in the genome of Pseudomonas syringae pv. tomato (Pto) DC3000, an important model in molecular plant pathology, with the aim of determining their physiological and possible non-canonical roles in this bacterium and in the plant infection process. We have established that the Gap1 protein has a predominantly glycolytic activity, whereas the NADPH-dependent Gap2 main activity is gluconeogenic. The third paralogue lacks GAPDH activity in Pto but is indispensable for vitamin B6 metabolism and displays erythrose-4-phosphate dehydrogenase activity, thus referred as epd. Both Gap enzymes exhibit distinct functional characteristics depending on the bacterium physiological state, with Gap1 presenting a substantial role in motility, biosurfactant production and biofilm formation. On the other hand, solely Gap2 appears to be essential for growth on tomato plant. Furthermore, Gap1 and Gap2 present a distinctive transcriptional regulation and both have been identified exported outside the cells with different definite media compositions. This serves as compelling evidence of additional roles beyond their central metabolic functions.

See https://pubmed.ncbi.nlm.nih.gov/37890268/

Fig. 4. Pto bacterial growth and symptom development. A. Growth and symptom development on tomato leaves inoculated with the deletion mutants. B. Growth and symptom development inoculated with the double mutant complemented with gap1 or gap2. Time course of growth of P. syringae gap mutants in the primary leaves of tomato plants (Solanum lycopersicum). Leaves were inoculated with approximately 10⁸ CFU/ml by spray and CFUs were quantified at 0, 3, 6 and 10 days post-inoculation (dpi). Error bars indicate standard deviation. Asterisks (*) indicate a statistically significant difference (Tuckey HSD test, p < 0.01). Pictures of the of symptoms induced on tomato leaves 10 dpi with the indicated strains.