Tissue-specific Regulation of Dihydrodipicolinate Synthase (DHDPS) Activity and Gene Expression in Medicago truncatula under Abiotic Stress

Abiotic stresses such as salinity and drought significantly reduce plant productivity worldwide. Dihydrodipicolinate synthase (DHDPS), a key enzyme in lysine biosynthesis, may play a crucial role in stress adaptation.

In this study, we examined the tissue-specific expression patterns of the DHDPS gene and its corresponding enzyme activity in Medicago truncatula exposed to salinity (200 mM NaCl) and osmotic (180 mM mannitol) stress. Hydroponically grown three- week-old plants were subjected to short-term (2 h) and prolonged (24 h) treatments. Gene expression was quantified using a rigorously optimized quantitative real-time PCR (qRT-PCR) protocol and data were analyzed using CFX Manager^TM software.

Our findings revealed a pronounced tissue-specific dichotomy in DHDPS expression and enzyme activity: transcript levels were significantly upregulated in roots (up to ~12-fold), while they were concurrently downregulated in leaves (by up to approximately half) across both stress conditions. Notably, root expression peaked under short-term mannitol exposure, suggesting a rapid and robust metabolic response likely linked to lysine-derived protective compounds. In contrast, the downregulation observed in leaves may reflect an energy-conserving strategy or a shift in metabolic priorities under stress. This distinct organ-specific regulation underscores the complexity of plant stress adaptation and offers promising avenues for targeted engineering of crop resilience.