Abstract

Granulation involves pectin demethylesterification and cellulose, little lignin. • Pectin accumulation is driven by upregulated PME and downregulated PG. • ABA rises, jasmonates fall in granulated sacs, suggesting hormonal regulation. • Candidate TFs coregulate wall and sugar–acid metabolism. • Our evidence supports the 'Disorder of cell wall metabolism' hypothesis in pomelo. Juice sac granulation severely impairs citrus postharvest quality, yet it remains unclear whether granulation already evident at harvest is governed by the same cell wall metabolic disorder described during storage. Here, ‘Dongshizao’ pomelo, which displays granulated juice sacs predominantly at the stem end while equatorial tissues remain normal at harvest, was used to investigate the biochemical and molecular basis of this spatial heterogeneity. Physiological measurements were integrated with transcriptomic, untargeted metabolomic, and targeted phytohormone analyses. Compared with equatorial normal juice sacs, stem-end granulated sacs had lower total soluble solids, titratable acidity, and juice yield, whereas relative water content was unchanged. Protopectin content and pectin methylesterase activity increased by 11.4% and 72.9%, respectively, while polygalacturonase activity decreased by 41.5%, indicating enhanced pectin demethylesterification and restricted pectin degradation. Cellulose biosynthesis-related genes, including CgCesA8 , were transcriptionally activated. Although lignin-pathway genes, particularly LAC and PRX family members, were induced, lignin content and most detected pathway intermediates did not increase significantly. Multi-omics integration further indicated coordinated reprogramming of sucrose and citrate metabolism, together with increased abscisic acid and decreased jasmonate-related metabolites. Co-expression analyses identified CgERF109 , CgERF99 , CgbHLH122 , CgMYB4 , and CgMYB52 as candidate regulators linking cell wall remodeling with sugar–acid metabol