Asparagine-Guided Regulation of Redox Status and Autophagy in Sugar-Starved Lupin (Lupinus spp.) Embryonic Axes—A Transcriptomic and Proteomic Approach

Sugar starvation during seed germination requires coordinated regulation of reserve mobilization, redox homeostasis, and intracellular recycling. In lupin seeds, asparagine is a major nitrogen-rich metabolite, but its role in starvation-induced autophagy and redox regulation remains unclear. Here, isolated embryonic axes of white lupin (Lupinus albus L.) and Andean lupin (Lupinus mutabilis Sweet) were cultured in vitro under sucrose-fed or sugar-starved conditions, with or without asparagine supplementation. Transcriptomic, proteomic, immunoblot, enzymatic, antioxidant activity, and confocal microscopy analyses were used to investigate ROS metabolism, antioxidant responses, autophagy, and vacuolar hydrolysis. Sugar starvation induced a catabolic response in both species, involving altered transcript abundance of genes encoding ROS-related proteins, increased catalase content, enhanced expression of many autophagy-related genes, and elevated proteolytic activity. Peroxisome-associated components, including glycolate oxidase, acyl-CoA oxidase, and catalase, were strongly affected, indicating dynamic remodeling of peroxisome-related metabolism during starvation. Asparagine markedly modified this response. In sugar-starved axes, it increased total antioxidant activity and catalase accumulation, while reducing the number of detectable autophagosomes, decreasing the transcript levels of many ATG genes, vacuolar proteases, and other vacuolar hydrolases, and lowering proteolytic activity. Together with previous evidence for asparagine-induced accumulation of autophagic bodies in vacuoles, these results suggest that asparagine may reorganize autophagy-related dynamics at multiple levels rather than acting at a single autophagic step. White and Andean lupin shared the same general regulatory framework but differed in response intensity. Andean lupin showed greater starvation-induced changes in the transcripts of genes encoding ROS-generating proteins, whereas white lupin displayed a clearer asparagine-dependent response of vacuolar hydrolases. Thus, asparagine links nitrogen status with redox stabilization, vacuolar catabolism, and autophagic flux in sugar-starved lupin embryonic axes.