The Relationship between the Expression of Ethylene-Related Genes and Papaya Fruit Ripening Disorder Caused by Chilling Injury

Papaya (Carica papaya L.) is sensitive to low temperature and easy to be subjected to chilling injury, which causes fruit ripening disorder. This study aimed to investigate the relationship between the expression of genes related to ethylene and fruit ripening disorder caused by chilling injury. Papaya fruits were firstly stored at 7°C and 12°C for 25 and 30 days, respectively, then treated with exogenous ethylene and followed by ripening at 25°C for 5 days. Chilling injury symptoms such as pulp water soaking were observed in fruit stored at 7°C on 20 days, whereas the coloration and softening were completely blocked after 25 days, Large differences in the changes in the expression levels of twenty two genes involved in ethylene were seen during 7°C-storage with chilling injury. Those genes with altered expression could be divided into three groups: the group of genes that were up-regulated, including ACS1/2/3, EIN2, EIN3s/EIL1, CTR1/2/3, and ERF1/3/4; the group of genes that were down-regulated, including ACO3, ETR1, CTR4, EBF2, and ERF2; and the group of genes that were un-regulated, including ACO1/2, ERS, and EBF1. The results also showed that pulp firmness had a significantly positive correlation with the expression of ACS2, ACO1, CTR1/4, EIN3a/b, and EBF1/2 in fruit without chilling injury. This positive correlation was changed to negative one in fruit after storage at 7°C for 25 days with chilling injury. The coloring index displayed significantly negative correlations with the expression levels of ACS2, ACO1/2, CTR4, EIN3a/b, ERF3 in fruit without chilling injury, but these correlations were changed into the positive ones in fruit after storage at 7°C for 25 days with chilling injury. All together, these results indicate that these genes may play important roles in the abnormal softening and coloration with chilling injury in papaya.

番木瓜（Carica papaya L.）对低温环境敏感，极易遭受冷害，进而引发果实成熟紊乱。本研究旨在探究乙烯相关基因的表达水平与冷害诱导的果实成熟紊乱之间的关联。本研究首先将番木瓜果实分别置于7℃与12℃条件下贮藏25天和30天，随后施加外源乙烯，并于25℃下后熟5天。贮藏于7℃的果实于20天时便出现果肉水渍状等冷害症状，而贮藏25天后的果实转色与软化过程完全受阻。在发生冷害的7℃贮藏果实中，22个乙烯相关基因的表达水平变化存在显著差异。这些表达发生改变的基因可分为三类：上调表达基因，包括ACS1/2/3、EIN2、EIN3s/EIL1、CTR1/2/3及ERF1/3/4；下调表达基因，包括ACO3、ETR1、CTR4、EBF2与ERF2；以及表达未发生显著变化的基因，包括ACO1/2、ERS与EBF1。研究结果还显示，在未发生冷害的果实中，果肉硬度与ACS2、ACO1、CTR1/4、EIN3a/b及EBF1/2的表达水平呈显著正相关；而在7℃贮藏25天发生冷害的果实中，这种正相关关系转变为负相关。此外，在未发生冷害的果实中，着色指数与ACS2、ACO1/2、CTR4、EIN3a/b、ERF3的表达水平呈显著负相关，但在7℃贮藏25天发生冷害的果实中，这些相关性均转变为正相关。综上，上述结果表明，这些基因可能在番木瓜冷害引发的果实异常软化与转色过程中发挥重要作用。