GLUL and viral infectious disease: GABA is synthesized from Glu by a decarboxylation reaction in response to abiotic stress, viral infection, and herbivore attack [58]; its increased concentration in BABA-treated tomato plants is almost certainly connected to the strong transcriptomic and proteomic upregulation of its key biosynthetic enzyme glutamate decarboxylase (Solyc04g025530.2.1) (Fig 5C).