NADP-malic enzyme 1 coordinates root development and seed vigor and longevity in <em>Arabidopsis thaliana</em>

Abstract

Plant growth and development depend on hormone signaling, reactive oxygen species (ROS) dynamics, and metabolic regulation. This thesis investigates NADP-dependent malic enzyme 1 (NADP-ME1) in <em>Arabidopsis thaliana</em>, focusing on its roles in root elongation and seed aging. <br/> In roots, NADP-ME1 is involved in ABA-induced inhibition of primary root elongation. Loss-of-function mutants show partial resistance to this effect, indicating that NADP-ME1 is required for full ABA sensitivity. Auxin reporter analyses show that NADP-ME1 is necessary for ABA-induced asymmetric auxin distribution, while cytokinin patterns remain largely unaffected. Pharmacological experiments implicate auxin transport, ethylene signaling, and Ca2⁺-dependent pathways in NADP-ME1-mediated responses. ROS imaging reveals altered superoxide accumulation in me1 mutants, linking NADP-ME1 to localized redox homeostasis. Transcriptomic profiling revealed selective regulation of ABA-responsive genes involved in redox balance, hormone signaling, and stress adaptation. Co-immunoprecipitation coupled with mass spectrometry (Co-IP-MS) and bimolecular fluorescence complementation (BiFC) identified ascorbate peroxidase 1 (APX1) and major latex protein-like protein 34 (MLP34) as NADP-ME1 interactors, connecting NADPH production to ROS detoxification regulation. <br/> In seeds, NADP-ME1 is involved in vigor and longevity after aging. Overexpression lines show higher germination rates, whereas loss-of-function mutants display reduced vigor. Improved performance of the overexpression lines correlates with lower ROS accumulation, reduced lipid peroxidation, preservation of polyunsaturated fatty acids, and increased γ-tocopherol levels, indicating enhanced membrane protection. NADP-ME1 overexpression alters the transcriptomic profile of germinated seeds under fresh conditions relative to the wild type, whereas only minor genotype-dependent differences are observed in aged seeds. These results suggest that NADP-ME1 contributes to the establishment of a transcriptional state associated with enhanced seed vigor and improved post-aging germination. After aging, key genes involved in lipid organization, detoxification, and ABA catabolism are selectively regulated. Protein interaction studies identify aspartate aminotransferase 2 (ASP2) as a direct partner, linking malate metabolism to carbon-nitrogen remodeling during recovery, while tryptophan-rich sensory protein (TSPO) emerge as potential components of a stress-response module. <br/> Overall, NADP-ME1 integrates metabolic, redox, and hormonal signaling to regulate root growth and preserve seed vigor and longevity after accelerated aging. In roots, it modulates auxin distribution and ROS homeostasis, whereas in seeds it limits oxidative damage and enhances metabolic resilience. Together these findings, provide mechanistic insight into how NADP-ME1 coordinates metabolism and redox balance to optimize plant performance.