Metabolome and Transcriptome Integration Reveals Insights Into Flavor Formation of 'Crimson' Watermelon Flesh During Fruit Development.

Chengsheng Gong,Xuqiang Lu,M O Kaseb,Pingli Yuan,Weinan Diao,Wenge Liu,Muhammad Jawad Umer,Shengjie Zhao,Muhammad Anees,Hongju Zhu,Dongdong Yang,Nan He

doi:10.3389/fpls.2021.629361

Abstract

Metabolites have been reported as the main factor that influences the fruit flavor of watermelon. But the comprehensive study on the dynamics of metabolites during the development of watermelon fruit is not up-to-date. In this study, metabolome and transcriptome datasets of ‘Crimson’ watermelon fruit at four key developmental stages were generated. A total of 517 metabolites were detected by ultrahigh-performance liquid chromatography–electrospray ionization–tandem mass spectrometry and gas chromatography–solid-phase microextraction–mass spectrometry. Meanwhile, by K-means clustering analysis, the total differentially expressed genes were clustered in six classes. Integrating transcriptome and metabolome data revealed similar expression trends of sugars and genes involved in the glycolytic pathway, providing molecular insights into the formation of taste during fruit development. Furthermore, through coexpression analysis, we identified five differentially expressed ADH (alcohol dehydrogenase) genes (Cla97C01G013600, Cla97C05G089700, Cla97C01G001290, Cla97C05G095170, and Cla97C06G118330), which were found to be closely related to C9 alcohols/aldehydes, providing information for the formation of fruit aroma. Our findings establish a metabolic profile during watermelon fruit development and provide insights into flavor formation.

Highlights

Flavor quality is one of the most important criteria for consumers to select vegetables and fruits (Barrett et al, 2010) and promotes customers’ desire for reconsumption
The most notable difference was that as watermelon fruits develop and ripen, the color of the flesh changes from light white to bright red (Figure 1A); at the same time, through taste evaluation, it was found that at 10 days after pollination (DAP), the taste of watermelon fruit was light, but at 34 DAP, the taste of watermelon became sweet and delicious; this corresponds to olfactory perception; at 124 DAMs were screened by comparing KL1 (10 DAP), the intensity of aroma was not much pleasant, but with a fresh and pleasant aroma at 34 DAP
An increasing trend was observed for TSS content at all development stages, i.e., 4.97, 7.87, 9.77, and 10.67 at 10, 18, 26, and 34 DAP (Figure 1C), respectively, whereas watermelon flesh’s firmness was measured as 2.72, 2.05, 1.68, and 1.27 kg/cm2 at 10, 18, 26, and 34 DAP (Figure 1D), which has an opposite trend compared with fruit weight and TSS. pH can reflect the change of watermelon acidity, high pH is consistent with low acidity. pH values were recorded as 4.95, 5.14, 5.33, and 5.66 at 10, 18, 26, and 34 DAP (Figure 1E), respectively, indicating a decrease in acidity during fruit development

Summary

Introduction

Flavor quality is one of the most important criteria for consumers to select vegetables and fruits (Barrett et al, 2010) and promotes customers’ desire for reconsumption. The flavor is typically described as a sum of the interactions between taste and aroma. The formation of flavor is the result of the interaction of multiple metabolites. Different fruits have different aromas that may result from a combination of multiple metabolites, Formation of Watermelon Flavor for instance, 2,6-nonadienal is the characteristic VOC in cucumber (Forss et al, 1962), but it is detected in other fruits with different fruit aromas. As the market demand for highquality fruit is a feature of modern consumer society, a more comprehensive understanding of fruit flavor-related metabolites and their improvement should be an important objective in breeding programs (Kyriacou and Rouphael, 2018)

Methods

Results

Discussion

Conclusion