Lysine biosynthesis impairment gives cues about connection with TCA cycle intermediates in Arabidopsis response to salt disturbance

Soil salinity is one of the most common environmental disturbances affecting plant growth and crop yield. To cope with high salt concentrations, plants have evolved various morphological, physiological, and biochemical strategies. A growing body of evidence highlights lysine as a key amino acid in the salinity response of plants. However, the roles of lysine biosynthesis and catabolism in response to salinity conditions remain poorly understood. In this study, we used Arabidopsis thaliana mutants with reduced activity of the enzyme L,L-diaminopimelate aminotransferase (dapat) and a T-DNA line of dihydropicolinate synthase (dhdps-2) to investigate the role of lysine in both physiological and metabolic responses to salinity. Overall, dapat mutant plants exhibited greater salt sensitivity, as indicated by lower seed germination rates, while dhdps-2 mutants showed greater salinity tolerance than wild-type ones. Progressive reductions in maximum photochemical efficiency values of photosystem II (Fv/Fm) were observed across all genotypes (mutants and their respective wild-types) under salinity conditions. Salt exposure also induced the accumulation of total amino acids, while reducing total protein and starch concentrations. Malate and fumarate exhibited differential dynamic profiles in the mutants under salinity conditions. Collectively, our results suggest that lysine biosynthesis homeostasis under salinity conditions may be linked to energy metabolism pathways. Although dhdps-2 and dapat mutations affect the same lysine biosynthetic pathway, these genes most likely play distinct roles in maintaining metabolic homeostasis in response to salinity.