目的 综合评价番石榴Psidium guajava不同品种间的果实品质差异并挖掘黄酮类化合物合成的关键基因。方法 对番石榴6个品种的11个果实品质指标进行测定，并结合主成分分析方法综合评价其品质差异，运用转录组测序技术比较各品种间的差异表达基因(Differentially expressed gene, DEG)，通过 GO 和 KEGG 富集分析，挖掘黄酮类化合物合成的DEG，利用实时荧光定量 PCR (Quantitative real-time PCR，qRT-PCR)研究DEG在不同品种间的特异性表达。结果 6种番石榴试材中‘金斗香’和‘胭脂红’品质最优，得分较高，‘水晶’和‘西瓜红’较低，‘珍珠’和‘红宝石’居中；‘金斗香’和‘胭脂红’的类黄酮质量分数较高，分别为9.76和10.05 mg/g，是‘水晶’(5.74 mg/g)的1.5倍以上，显著高于其他品种(P>0.05)。转录组测序分析显示，‘金斗香’和‘胭脂红’的DEG聚为一类，其余4种的DEG聚为一类。黄酮类化合物的生物合成途径中CHS、FLS、CYP73A、CYP98A3、DFR、E184.108.40.206、E220.127.116.11和CYP75A基因在‘金斗香’和‘胭脂红’中表达量显著上调。qRT-PCR验证结果表明，FLS基因在‘胭脂红’中表达量最高，是‘西瓜红’的10倍以上；CYP73A、CYP75A、E18.104.22.168和CHS基因在‘金斗香’中表达量最高，‘珍珠’中表达量最低，其中CYP73A和CYP75A基因在‘金斗香’中的表达量是‘珍珠’的30倍以上；而DFR基因在‘胭脂红’中表达量较高，‘金斗香’中表达量较低。qRT-PCR检测到DEG的表达水平与转录组测序结果一致，证明番石榴6个品种的转录组测序结果可靠。结论 本研究系统评价了6种番石榴果实品质差异，并挖掘到8个与番石榴黄酮类化合物合成相关的关键基因，为后期番石榴的品种选育、功能基因挖掘和黄酮类化合物的生物合成途径等研究提供科学依据。
Objective The purpose of this study was to comprehensively evaluate the differences in fruit quality among different guava (Psidium guajava) cultivars and explore key genes for flavonoid synthesis. Method A total of 11 fruit quality indexes of six guava cultivars were measured and principal component analysis was carried out. Transcriptome sequencing technology was used to compare the differentially expressed genes (DEGs) among the cultivars, and GO and KEGG enrichment analyses were carried out to mine the DEGs of flavonoid synthesis. Quantitative real-time PCR (qRT-PCR) was used to study the specific expression of differential genes in different cultivars. Result Among the six guava cultivars, ‘Jindouxiang’ and ‘Yanzhihong’ scored higher, ‘Shuijing’ and ‘Xiguahong’ scored lower, and ‘Zhenzhu’ and ‘Hongbaoshi’ scored in the middle. The flavonoid contents of ‘Jindouxiang’ and ‘Yanzhihong’ were significantly higher compared to other cultivars (P>0.05), which were 9.76 and 10.05 mg/g, respectively, more than 1.5 times that of ‘Shuijing’ (5.74 mg/g). Transcriptome sequencing analysis showed that the DEGs of ‘Jindouxiang’ and ‘Yanzhihong’ were clustered into one category, and the DEGs of the other four cultivars were clustered into one category. CHS, FLS, CYP73A, CYP98A3, DFR, E22.214.171.124, E126.96.36.199 and CYP75A genes in the biosynthetic pathway of flavonoids were significantly up-regulated in ‘Jindouxiang’ and ‘Yanzhihong’. qRT-PCR verification showed that the expression of FLS gene was the highest in ‘Yanzhihong’, which was more than 10 times of that in ‘Xiguahong’. The expression levels of CYP73A, CYP75A, E188.8.131.52 and CHS genes were the highest in ‘Jindouxiang’ and the lowest in ‘Zhenzhu’. Among them, the expression levels of CYP73A and CYP75A genes in ‘Jindouxiang’ were more than 30 times of those in ‘Zhenzhu’, while the expression level of DFR gene was higher in ‘Yanzhihong’ and lower in ‘Jindouxiang’. The expression levels of DEGs were consistent comparing the qRT-PCR and transcriptome sequencing results, indicating the transcriptome sequencing results of six guava cultivars were reliable. Conclusion The quality differences of six guava cultivars were systematically evaluated, and eight key genes related to the synthesis of guava flavonoids were discovered. This study provides a scientific basis for the research of guava cultivar breeding, functional gene mining and biosynthetic pathway of flavonoids.