苹果绵肉与脆肉株系果实质地差异的分子机理

【目的】研究新疆红肉苹果（Malus sieversii脆2号’ f. neidzwetzkyana）与‘富士’苹果品种（M. domestica cv. Fuji）杂交后代绵/脆肉株系果实质地差异的分子机理，旨在为进一步完善功能型苹果育种的理论与技术体系提供科学依据。【方法】以新疆红肉苹果杂交后代‘红绵2号’和‘红脆2号’不同发育时期的果实为试材，检测乙烯释放量、果实硬度与脆度以及ACS1等4个乙烯生物合成基因和PG等30个果实软化相关基因的相对表达量，观察其变化。【结果】‘红绵2号’和‘红脆2号’苹果果实发育期间的硬度和脆度均呈下降趋势，但‘红脆2号’各时期果实硬度和脆度均明显高于‘红绵2号’。‘红绵2号’花后120 d乙烯释放速率明显上升，并出现明显的乙烯释放峰；而‘红脆2号’花后120 d乙烯释放速率上升不明显，且无明显的乙烯释放峰。‘红苹果果实各时期的ACS1、ACS3、ACO1和ACO2 4个乙烯生物合成相关基因表达量均明显低于‘红绵2号’；4个乙烯生物合成相关基因的表达模式存在明显差异，其中‘红绵2号’ACS1、ACO1和ACO2三个基因在果实发育后期的表达量均在94%以上，而ACS3a在果实发育前、后期表达量分别占50%，表现为组成型表达。所检测的与果实软化相关的30个基因表达的时间顺序存在明显差异，其中PL、AF1、EG2及XET1等15个基因主要在果实发育前期表达，PG、AF3、XET2、XET10和XET11 5个基因主要在果实发育后期表达，基因表达量均占总表达量的70%以上；除PL和AF1等6个基因外，‘红脆2号’PG等24个基因的总表达量均极显著低于‘红绵2号’。【结论】果实发育后期乙烯释放高峰的到来以及果实发育前、后期不同乙烯生物合成与果实软化相关基因的上调表达，是导致‘红绵2号’果实在采收前就已软化变绵及其与‘红脆2号’质地差异的主要原因。

Study on the Molecular Mechanism Controlling Differences in Fruit Texture Formation of Apple Soft/Crisp Strains

【Objective】In order to perfect the breeding theory and technology system of functional apple, the molecular mechanism controlling differences in fruit texture formation of soft/crisp strains from the cross progenies of ‘Fuji’ and M. sieversii f. neidzwetzkyana was studied. 【Method】The ethylene production, fruit firmness, crispness, the relative expression intensity of 4 genes related to ethylene biosynthesis (ACS1 etc.) and 30 genes related to fruit softening (PG) were detected in fruits of different development stages of two cross progenies of ‘Fuji’ and M. sieversii f. neidzwetzkyana (‘Hongmian2’ and ‘Hongcui2’). 【Result】Fruit firmness and crispness both declined during development period in both ‘Hongmian2’ and ‘Hongcui2’, but fruit firmness and crispness of ‘Hongcui2’ was significantly higher than that in ‘Hongmian2’ all the time. The ethylene production of ‘Hongmian2’ increased at DAFB 120 d and presented a peak of ethylene production, while the ethylene production of ‘Hongcui2’ didn’t increase significantly at DAFB 120 d and had no obvious peak. The expression patterns of 4 ethylene biosynthesis genes were different. The expression of ACS1, ACO1 and ACO2 in ‘Hongmian2’ during late development period weighed over 94%, while ACS3a showed constitutive expression, occupying 50% of total expression during early and late development period, respectively. The expression periods of 30 genes related to fruit softening were different. With over 70% of the total expression, 15 genes (PL, AF1, EG2 and XET1 etc.) and 5 genes (PG, AF3, XET2, XET10 and XET11) mainly expressed during early development and late development period, respectively. Except 6 genes (PL, AF1 etc.), the expression of other 24 genes (PG etc.) in ‘Hongcui2’ was significantly lower than that in ‘Hongmian2’. 【Conclusion】The appearance of ethylene production peak during late development period and the up-regulated expression of genes related to ethylene biosynthesis and fruit softening during early and late development period resulted in the softening of ‘Hongmian2’ before harvest and the texture difference between ‘Hongmian2’ and ‘Hongcui2’.