Integrated physiological and transcriptomic analyses reveal cell wall remodeling underlying firmness retention in a...

Fruit softening is a major factor limiting the postharvest quality, transportability, and shelf life of blueberry, but the physiological and molecular basis of firmness variation remains incompletely understood.

The soft-fruited cultivar 'Duke' and the firm-fruited genotype '2017D' were compared using phenotypic, physiological, histological, biochemical, transcriptomic, and transient functional analyses.

'2017D' maintained substantially higher firmness during fruit development, together with greater retention of several texture attributes, including chewiness, gumminess, resilience, and cohesiveness. Histological observations showed that '2017D' retained a comparatively more continuous mesocarp organization at the blue stage. Cell wall analysis further revealed greater retention of structural polysaccharides and insoluble pectin in '2017D', whereas 'Duke' accumulated more soluble pectin during the later developmental stages. Lower PG and β-galactosidase activities in '2017D' were consistent with reduced cell wall polysaccharide degradation during ripening. RNA-seq analysis identified 6,168 differentially expressed genes between the two genotypes, with significant enrichment of pathways and biological processes associated with hormone signaling, carbohydrate metabolism, cell wall organization, and related ripening processes. Among the cell wall-related candidate genes, VcβGAL369 showed a pronounced expression difference between the two genotypes and a distinct developmental expression pattern and was therefore selected for further characterization. Transient silencing of VcβGAL369 increased fruit firmness and promoted cell wall component retention, whereas transient overexpression reduced fruit firmness and promoted cell wall disassembly.

These results indicate that the contrasting firmness of '2017D' and 'Duke' is associated with differences in cell wall remodeling and ripening-related transcriptional processes and support a role for VcβGAL369 in promoting blueberry fruit softening.