裂果性不同的番荔枝品种果皮中细胞壁代谢相关基因的表达分析

Expression analysis of cell wall metabolism gene in pericarp of custard apple cultivars with different fruit cracking characters

【目的】探讨细胞壁代谢相关基因在裂果品种(AP番荔枝)和不裂果品种(PO番荔枝)采后贮藏期间的表达差异。【方法】对番荔枝2个品种采后后熟不同阶段以及对AP番荔枝进行喷施乙烯利处理后对果皮进行取样,测定果实硬度和可溶性固形物含量,利用实时荧光定量PCR技术检测8个细胞壁代谢相关基因在2个品种室温贮藏期间和乙烯利处理后,基因在不同阶段的表达变化,并应用CLUSTER软件对基因的差异表达进行双向层次聚类分析。【结果】AP番荔枝和PO番荔枝采后后熟期间的可溶性固形物含量和硬度值变化基本一致,2者之间无明显差异,而乙烯利处理能加速AP番荔枝的成熟与开裂。定量PCR分析表明,贮藏期间8个基因在PO番荔枝中的表达量均低于AP番荔枝,其中PPO在PO番荔枝中无表达,EXP2、EXP3和PE在PO番荔枝贮藏期前3 d表达量很低。EXP1在2个番荔枝品种贮藏期间一直处于高水平表达,但不受外源乙烯诱导,而EXP2、EXP3、XET1、XET3、PE和PPO均不同程度受到乙烯诱导。大多数基因在第1天,果实开裂前表达量已增加,随着裂果的加重表达量下降。聚类分析表明在PO番荔枝后熟过程中发生剧烈变化的有EXP1、EXP2、EXP3和PE基因,在AP-正常和AP-乙烯裂果前后表达量变化比较剧烈的基因基本一致,包括EXP1、EXP2、EXP3、PPO和PE。【结论】EXP1更多和果实成熟软化有关。EXP2、EXP3、PE和PPO与裂果关系较为密切,而XET1、XET2和XET3可能与果实成熟软化有一定关系,但不是果实开裂的关键基因。

【Objective】To demonstrate the expression differences of cell wall metabolism related genes in custard apples with different fruit cracking characters（susceptible and resistant to fruit cracking） during postharvest storage.【Methods】We sampled pericarp of two custard apple cultivars in different postharvest ripening stages and with ethephon treatment on AP custard apple,determined the fruit-firmness and soluble solid content,and analyzed expression difference of EXP1,EXP2,EXP3,XET1,XET2,XET3,PE,and PPO between custard apples susceptible and resistant to fruit cracking during storage,and compared expression difference of eight genes between normal temperature storage and ethephon treated AP custard apple. Furthermore,gene expression under different treatment or storage period was analysised by bidirectional hierarchical clustering using CLUSTER software.【Results】Results showed that soluble solids content and firmness had no obvious difference between AP and PO custard apple during the postharvest ripening period,and ethephon treatment accelerated the maturity and cracking of AP custard apple. Quantitative PCR analysis showed that expression levels of eight cell wall metabolism related genesin PO custard apple were always lower than that of AP during the whole storage period,in which the expression level of PPO stayed low in PO,and the expression level of EXP2,EXP3,PE were very low in the first three days in PO. EXP1 maintained a high expression level in the two custard apple cutivars,andis not induced by exogenous ethylene treatment,EXP2,EXP3,XET1,XET3,PE and PPO were induced by ethylene at different levels. The expression levels of most genes had increased in the first day before fruit cracking,decreased with the fruit cracking seriously. Clustering analysis showed that the expression level of EXP1,EXP2,EXP3 and PE in PO had dramatic changes during postharvest ripening period,and the genes in normal temperature storage which expression level had dramatic changes before and after AP custard apple softening and cracking were consistent with those in ethephon treatment,including EXP1,EXP2,EXP3,PPO and PE.【Conclusion】EXP1 was more relevant with fruit maturity and softening. EXP2,EXP3,PE and PPO had relatively close relations with fruit cracking,while XET1,XET2 and XET3 might have some relations with fruit softening,they could not be key genes of fruit cracking.