Mango Fructokinases Inhibit Sugar Accumulation and Enhance Energy Metabolism in Transgenic Tomato

Sugar content critically determines mango fruit quality and varies significantly among varieties. Preliminary studies indicate that <i>fructokinases</i> (<i>MiFRKs</i>) <i>MiFRK1</i> and <i>MiFRK2</i> likely regulate intervarietal sugar variation. We characterized these <i>MiFRKs</i> using heterologous expression in tomato. Both isoforms phosphorylate fructose, promoting downstream catabolism, with <i>R-MiFRK2</i> (from low-sugar 'Renong No. 1') exhibiting higher activity than <i>T-MiFRK2</i> (high-sugar 'Tainong No. 1') and <i>MiFRK1</i>. Transcriptomic and metabolic analyses reveal that <i>MiFRK</i> overexpression inhibits sugar accumulation by altering the expression of key metabolic genes, including sucrose degradation enzymes (<i>invertases</i>), starch breakdown genes (<i>β-amylases</i>), and glycolytic genes (<i>enolases</i>). Intriguingly, <i>MiFRK1</i> and <i>MiFRK2</i> exhibit distinct regulatory effects on these pathways, suggesting functional specialization between the two isoforms. These findings provide novel insights into the molecular mechanisms through which <i>MiFRKs</i> govern sugar metabolism in mango, highlighting their potential as key targets for metabolic engineering to enhance fruit quality.