Multi-omics analysis reveals galactose metabolism as a key regulatory pathway of stress adaptation to magnesium deficiency in passion fruit.

Magnesium (Mg) deficiency is a major nutritional constraint in acidic orchard soils and can impair both vegetative growth and fruit quality in passion fruits (Passiflora edulis). However, the physiological and molecular mechanisms underlying Mg deficiency responses in passion fruit remain insufficiently understood. This study employed a comprehensive approach, integrating physiological assessments with metabolomic and transcriptomic profiling, to explore the responses to Mg deficiency in the leaves and fruits of purple passion fruit. Our findings revealed that Mg deficiency detrimentally affected chloroplast ultrastructure, significantly decreased SPAD values by an average of 16.1% and net photosynthetic rates by an average of 55.0% in leaves, and led to the accumulation of starch and soluble sugars (increased by approximately 26.4% and 11.9%, respectively) in source leaves. In fruit peels, Mg deficiency resulted in a significant reduction in anthocyanin content by approximately 46.3% and a 2.4-fold increase in chlorophyll content, leading to a 79.5% decrease in the anthocyanin-to-chlorophyll ratio and producing a commercially undesirable green coloration. Through integrative multi-omics analysis, we identified the specific alteration of the galactose metabolism pathway under Mg deficiency, which facilitated the synthesis of melibiose, fructose, and succinate as potential osmoprotectants. These results suggest that Mg deficiency compromises both the marketable appearance and nutritional quality of passion fruit, while simultaneously triggering carbon reallocation as an underlying potential mechanism. In conclusion, the metabolism of galactose may enhance plant adaptation to magnesium deficiency stress, thereby offering a physiological foundation for developing optimal magnesium fertilization strategies in passion fruit orchards cultivated in acidic soils.