4.1. Transcriptomic evidences of cold stress in young apple fruit undergoing abscission
The RNA-seq analysis provided potential evidences that the apple fruit collected in the latter part of May 2018 not only underwent abscission but were cold-stressed as well (Supporting Information Table S1). For example, the expression of dehydrin 1 (DHN1 ) homologMD02G1140100 , a cold stress marker, was down-regulated. Dehydrins are categorized into the LEA family, which contribute to cold tolerance. Although MdDHN1 was up-regulated in the ‘abscission’ group,dehydrin xero 1 (XERO1 ) homolog MD02G1139900 was rather down-regulated. The earlier study demonstrated that DHN1responds to low temperature and XERO1 is induced by drought, not by cold in peach (Bassett et al., 2009).Therefore, in our study, the up-regulation of DHN1 seemed to be a result of the cold stress response. Besides, in the oxidation-reduction category, two RuBPChomolog genes were up-regulated in the ‘abscission’ group. RuBPCsare known to make plants more susceptible to thermal variation in response to chilling stress (Gao et al., 2013).