Carbohydrate dynamics and transcriptomic changes during floral development in heterodichogamous Ziziphus jujuba

Flower opening is driven by petal cell elongation, a process that depends on water influx into cells and the maintenance of turgor pressure. Consequently, carbohydrate metabolism is fundamental to flower development, yet its role during floral development in heterodichogamous species remains poorly understood. In this study, we investigated biomass accumulation across the unopened flower bud, male, and female floral phases in the Early and Late morphs of Ziziphus jujuba. We further characterized non-structural carbohydrate dynamics and transcriptomic changes in flowers and corresponding leaf tissues across these developmental stages. Flower fresh weight, dry weight, and water content increased progressively during development, accompanied by significant accumulation of soluble sugars and starch from unopened buds to the male phase, whereas leaf carbohydrate levels remained relatively stable. Transcriptomic profiling showed pronounced tissue-specific expression patterns, with flowers exhibiting more extensive changes in gene expression than leaves, particularly during early developmental transitions in the Late morph. Functional enrichment and weighted gene co-expression network analysis (WGCNA) identified flower-specific co-expression modules that were positively correlated with soluble sugar and starch accumulation and enriched in carbon metabolism, glycolysis/gluconeogenesis, and nucleotide sugar metabolism. Moreover, the candidate genes g1pa, hex1, fba, and ugd1, which are annotated as participating in starch biosynthesis, glycolysis, and nucleotide sugar metabolism, displayed distinct stage-specific expression patterns. Together, these findings support a close association between carbohydrate dynamics and transcriptional changes during floral development and sex-phase transitions, providing new insights into these processes in the heterodichogamous species Z. jujuba.