Evaluation of guava fruit quality and mining of genes related to flavonoid synthesis

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, E2.1.1.104, E1.14.11.19 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, E2.1.1.104 and CHS genes were the highest in ‘Jindouxiang’ and the lowest in ‘Zhenzhu’. Among them, the expression levels ofCYP73A 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.