Comparative Proteomic Analysis Reveals Key Proteins Linked to the Accumulation of Soluble Sugars and Organic Acids in the Mature Fruits of the Wild Malus Species.

Baiquan Ma,Fengwang Ma,Mingjun Li,Yuduan Ding,Yangyang Yuan,Cuiying Li

doi:10.3390/plants8110488

Baiquan Ma, Fengwang Ma + Show 4 more

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https://doi.org/10.3390/plants8110488

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Abstract

Soluble sugars and organic acids are the main determinants of fruit organoleptic quality. To investigate the genes responsible for the soluble sugar and organic acid contents of apple fruits, a label-free proteomic analysis involving liquid chromatography (LC)-mass spectrometry (MS)/MS was conducted with the fruits of two Malus species, M. sargentii and M. niedzwetzkyana, which exhibit significant differences in soluble sugar and organic acid contents. A total of 13,036 unique peptides and 1,079 differentially-expressed proteins were identified. To verify the LC-MS/MS results, five candidate proteins were further analyzed by parallel reaction monitoring. The results were consistent with the LC-MS/MS data, which confirmed the reliability of the LC-MS/MS analysis. The functional annotation of the differentially-expressed proteins, based on the gene ontology and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases, revealed that they were mainly related to biological processes and cellular components. Additionally, the main enriched KEGG pathways were related to metabolic processes. Moreover, 31 proteins involved in soluble sugar metabolism, organic acid metabolism, and H+-transport were identified. The results of this study may be useful for the comprehensive characterization of the complex mechanism regulating apple fruit-soluble sugar and organic acid contents.

Highlights

Soluble sugars and organic acids are crucial determinants of fruit tastes, which combine with aromas to considerably influence the overall organoleptic quality of fruits [1,2]
Label-free proteomic techniques based on liquid chromatography (LC)-mass spectrometry (MS)/MS, which is widely used for quantitative analyses of protein expression, overcome the shortcomings of the traditional methods that cannot quantify proteins [19]
A label-free proteomic analysis involving LC-MS/MS was performed to investigate the accumulation of soluble sugars and organic acids in the fruits of two wild apple species

Summary

Introduction

Soluble sugars and organic acids are crucial determinants of fruit tastes, which combine with aromas to considerably influence the overall organoleptic quality of fruits [1,2]. Three major organic acids (malic, citric, and tartaric acids) accumulate in most fruits, and their concentration in mature fruits is determined by the balance among acid synthesis, degradation, utilization, and compartmentalization in subcellular organelles [6,7]. The predominant organic acids in mature fruits vary among species. Malic acid is the major organic acid in apple, loquat, and pear [2,8,9,10], whereas citric acid is the predominant organic acid in citrus fruits [11]

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