• Starch degradation correlates with mealiness in apple and accelerates texture loss. • Expression of genes of starch hydrolysis drive mealiness development dynamically. • β-amylase (BAM) promotes apple fruit mealiness via starch degradation regulation. • Cell wall hydrolases synergistically remodel parenchyma structure during mealiness. • Transcription factors mediate crosstalk between starch and cell wall metabolism. Starch degradation is considered a characteristic trait of apple ripening, but its relationship with flesh mealiness remains unclear. To address this, starch degradation in textural alterations of ‘Red Delicious’ apples at two maturity stages (ready-to-pick and ready-to-eat) were comparatively investigated. Histological and ultrastructural observations indicated that the mealiness occurred in the apple fruit harvested at both stages, though with different periods. The results obtained from either native starch-dying with iodine or chemical stoichiometry suggested the close correlation of starch content, activities of α -amylase (AMY) and β -amylase (BAM), with the progress of mealiness. Transcriptomic profiling revealed that starch and sucrose metabolism were much highly enriched during apple mealiness. Transcription of genes of MdBAM, MdMES1 , and MdpGlcT4 , associated with starch metabolic pathway, were up-regulated. Weighted correlation network analysis identified co-expressed modules linking cell wall hydrolases and starch degradation enzymes including BAM to mealiness. The transcription factors MdERF and MdNAC exhibited synchronized expression patterns with starch metabolic genes, suggesting their functions in coordinating mealiness and starch metabolism. Collectively, the results obtained from our work suggested that starch degradation contributed most to the mealiness of apple fruit. This interplay suggests that starch breakdown accelerates textural alterations not independently, but through synergistic crosstalk with cell wall remodeling and is proportional to maturity. Our findings thus provide a framework for understanding postharvest mealiness as a process driven by both starch metabolism and cell wall dynamics, offering novel targets for modulating fruit texture retention.
Li et al. (Thu,) studied this question.