Title of
Journal：
Postharvest Biology and Technology
Paper
Code：
Volume：
242
Number：
Page：
242:114587
Others：
Classification：
Source：
Abstract：
Postharvest thickening of solid endosperm (SE, coconut meat) is a distinct physiological phenomenon in coconut (Cocos nucifera L.) that affects fruit quality and seed germination, yet the underlying mechanism remains largely unknown. Here, by integrating physiological and biochemical analyses, we revealed that this thickening is associated with net accumulation of cellulose and hemicellulose (HEM, predominantly galactomannan). Transcriptome profiling identified two candidate genes involved in galactomannan metabolism: CnAGAL2 encoding an alpha-galactosidase and CnMAN6 encoding an endo-(3-mannanase. Both genes were transcriptionally down-regulated during storage, in parallel with a progressive decline in total alpha-galactosidase and (3-mannanase activities. Functional validation via recombinant protein expression and transient overexpression in tobacco leaves demonstrated that CnAGAL2 possesses strong alpha-galactosidase activity, whereas CnMAN6 showed no detectable (3-mannanase activity. During postharvest storage, reduced CnAGAL2 expression suppressed HEM degradation; meanwhile, the upregulation of cell wall biosynthetic genes further contributed to the net accumulation of cellulose and HEM, leading to SE thickening. Phylogenetic analysis indicated that CnAGAL2 belongs to the GH27 family, and subcellular localization confirmed that it is targeted to the cell periphery. Promoter analysis revealed enrichment of abscisic acid (ABA)-responsive elements, and a dual-luciferase assay showed that exogenous ABA significantly repressed the CnAGAL2 promoter. These findings provide a molecular basis for postharvest endosperm thickening in coconut and offer insights into HEM metabolism in recalcitrant seeds.
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