Transcriptome Analyses Reveal the Mechanisms of Mature Plum Fruit Cracking. Prunus salicina

Fruit cracking is a well-known preharvest disorder in plum production that has been studied at the physiological, biochemical, and molecular levels in many plants. Nevertheless, the molecular mechanism of fruit cracking in plums remains uncertain. Cracked and non-cracked fruits were collected from a greenhouse and open field for transcriptome analyses. The starch, sugar, and hormone pathways overlapped between the two models. Differentially expressed genes involved in starch, sugar, and pectin metabolism were further analyzed and the results showed that four starch-biosynthesis genes were significantly downregulated, while three degradation-related genes were upregulated in cracked fruits, coinciding with changes in starch content. Five sugar-biosynthesis genes were upregulated in cracked fruits, which had significantly higher soluble sugar contents. The downregulation of five pectin-biosynthesis genes and upregulation of three degradation genes were also observed, along with changes in protopectin and soluble pectin contents. Based on gene expression and material content analyses, we speculate that the conversion of starch into sugars and pectin degradation are the key intrinsic factors driving plum fruit cracking, with the former increasing turgor pressure and leading to cell and tissue rupture, which latter destroys the mechanical strength and toughness of the cell wall.