Changes in calcium content and expression of calcium sensor-related genes during sand pear (Pyrus prifolia) fruit cracking

Fruit cracking is a physiological disorder and results in significant economic losses. Calcium (Ca) plays important roles in the pear fruit cracking process, however, the underlying molecular mechanism of fruit cracking induced by Ca is poorly understood. In the present study, using cracking susceptible pear genotype '4-5-73 ', we inves-tigated the changes in Ca content and Ca sensors-related gene expression in the peel and flesh samples of cracked and non-cracked fruit. Cracking symptoms started to appear on the peel at 9 weeks after anthesis (WAA), and the total cracking rate gradually increased during fruit development until 15 WAA. During the early fruit cracking period (9 to 12 WAA), the Ca content in the peel and flesh of cracked fruit was lower than that of non-cracked fruit. Transcriptome sequencing indicated that 17 Ca sensors-related genes were differentially expressed in cracked and non-cracked fruit peel at 13 WAA. Among them, PpCML11 displayed higher expression in the peel and flesh of cracking fruit than that of non-cracked fruit. In addition, a positive correlation was observed between the PpCML11 expression level and the Ca content in the flesh of non-cracked fruit. Taken together, the present study suggests that PpCML11 might be involve in the sand pear flesh development process, and could play an important role in response to biotic stress after fruit cracking.