Distinct Mg²⁺ responses and species-specific transcriptional regulation of the magnesium transporter MGR2 in Saccharum officinarum and Saccharum spontaneum

Abstract Background Magnesium (Mg²⁺) is essential for chlorophyll synthesis, enzyme activation, and photosynthesis, but the differential regulation of Mg²⁺ homeostasis between the two founding Saccharum species ( Saccharum officinarum and Saccharum spontaneum ) remains unknown. Results We systematically characterized the MGR gene family in S. spontaneum and S. officinarum and uncovered distinct physiological responses to Mg²⁺ availability between the two species. Comparative expression analysis across the leaf developmental gradient and diurnal cycles revealed species-specific transcriptional dynamics of MGR2 , suggesting divergent regulatory mechanisms underlying Mg²⁺ management. Functional complementation in the Mg²⁺-deficient Salmonella typhimurium MM281 mutant demonstrated that both SsMGR2 and SoMGR2 restore Mg²⁺ uptake, confirming their conserved transport capability. Overexpression of SsMGR2 in rice conferred increased biomass under Mg²⁺ deficiency and enhanced tolerance to Mg²⁺ excess, indicating a broad role for this gene in Mg²⁺ homeostasis. Promoter architecture and transcription factor prediction further revealed interspecific divergence, with BBX25, COL5, and WRKY19-2 exhibiting species-dependent regulatory interactions that potentially explain the observed differences in MGR2 expression. Conclusion Overall, the research results indicate that S. spontaneum and S. officinarum exhibit different Mg²⁺ responses and MGR2 regulatory patterns, highlighting the distinct strategies for Mg²⁺ homeostasis in these two founding species. This work provides new insights into the transport mechanism of Mg²⁺ in sugarcane and preliminarily identifies candidate genes and regulatory factors for improving nutrient efficiency and stress recovery ability.