Screening of cell wall-related genes that are expressed differentially during ripening of pears with different softening characteristics

Abstract Postharvest softening is an important physiological process that influences pear fruit quality. ‘Starkrimson’ pears soften rapidly, resulting in fruits with a low tolerance for storage and transportation. To better characterize the mechanism regulating the rapid softening of pears, cell wall-related changes were compared among three soft-fleshed and rapid-softening cultivars (‘Starkrimson’, ‘Bartlett’, and ‘Abbe Fetel’) and a crisp-fleshed and non-softening cultivar (‘Dangshansuli’). Cell wall polysaccharide content measurements revealed that rapid fruit softening was accompanied by extensive pectin degradation in the three soft-fleshed cultivars. Fifteen genes encoding two polygalacturonases (PG; EC 3.2.1.15), four pectin methylesterases (EC 3.1.1.11), four β-galactosidases (EC 3.2.1.23), one α-L-arabinofuranosidase (EC 3.2.1.55) and four cellulases (EC 3.2.1.4) were isolated from pear fruit flesh. Gene expression analyses indicated that almost all of the genes were involved in ripening. Furthermore, PG2 exhibited the most significant expression-level differences between the two types of pears, suggesting it was responsible for the rapid softening of the three soft-fleshed pears. PG1 was highly expressed only in ‘Starkrimson’ pears, which may explain the considerably faster softening rate of ‘Starkrimson’ fruits compared with those of other cultivars. Additionally, 1-methylcyclopropene (1-MCP) was used to control the softening rate of ‘Starkrimson’ pears, PG1 and PG2 expression was effectively inhibited by 1-MCP. The results of this study suggest that PG genes have crucial roles in the rapid softening of ‘Starkrimson’ pears.