Chang Hsueh-Yuan, Tong Cindy B S
Department of Horticultural Science, University of Minnesota, Saint Paul, MN 55108, USA.
Plants (Basel). 2020 Oct 10;9(10):1335. doi: 10.3390/plants9101335.
Crispness retention is a postharvest trait that fruit of the 'Honeycrisp' apple and some of its progeny possess. To investigate the molecular mechanisms of crispness retention, progeny individuals derived from a 'Honeycrisp' × MN1764 population with fruit that either retain crispness (named "Retain"), lose crispness (named "Lose"), or that are not crisp at harvest (named "Non-crisp") were selected for transcriptomic comparisons. Differentially expressed genes (DEGs) were identified using RNA-Seq, and the expression levels of the DEGs were validated using nCounter. Functional annotation of the DEGs revealed distinct ripening behaviors between fruit of the "Retain" and "Non-crisp" individuals, characterized by opposing expression patterns of auxin- and ethylene-related genes. However, both types of genes were highly expressed in the fruit of "Lose" individuals and 'Honeycrisp', which led to the potential involvements of genes encoding auxin-conjugating enzyme (GH3), ubiquitin ligase (ETO), and jasmonate O-methyltransferase (JMT) in regulating fruit ripening. Cell wall-related genes also differentiated the phenotypic groups; greater numbers of cell wall synthesis genes were highly expressed in fruit of the "Retain" individuals and 'Honeycrisp' when compared with "Non-crisp" individuals and MN1764. On the other hand, the phenotypic differences between fruit of the "Retain" and "Lose" individuals could be attributed to the functioning of fewer cell wall-modifying genes. A cell wall-modifying gene, , was consistently identified as differentially expressed in those fruit over two years in this study, so is a major candidate for crispness retention.
保持脆度是“蜜脆”苹果及其一些后代果实所具有的采后特性。为了研究保持脆度的分子机制，从“蜜脆”×MN1764群体中挑选出果实具有保持脆度（命名为“保持型”）、失去脆度（命名为“失去型”）或采收时不脆（命名为“非脆型”）的后代个体进行转录组比较。使用RNA-Seq鉴定差异表达基因（DEG），并使用nCounter验证DEG的表达水平。对DEG的功能注释揭示了“保持型”和“非脆型”个体果实之间不同的成熟行为，其特征是生长素和乙烯相关基因的表达模式相反。然而，这两类基因在“失去型”个体和“蜜脆”果实中均高表达，这导致编码生长素结合酶（GH3）、泛素连接酶（ETO）和茉莉酸O-甲基转移酶（JMT）的基因可能参与调节果实成熟。细胞壁相关基因也区分了表型组；与“非脆型”个体和MN1764相比，“保持型”个体和“蜜脆”果实中有更多的细胞壁合成基因高表达。另一方面，“保持型”和“失去型”个体果实之间的表型差异可归因于较少的细胞壁修饰基因的作用。在本研究中，一个细胞壁修饰基因在两年内的这些果实中一直被鉴定为差异表达，因此是保持脆度的主要候选基因。
