Proteomic Characterization of Differential Abundant Proteins Accumulated between Lower and Upper Epidermises of Fleshy Scales in Onion (Allium cepa L.) Bulbs

Abstract

The onion (Allium cepa L.) is widely planted worldwide as a valuable vegetable crop. The scales of an onion bulb are a modified type of leaf. The one-layer-cell epidermis of onion scales is commonly used as a model experimental material in botany and molecular biology. The lower epidermis (LE) and upper epidermis (UE) of onion scales display obvious differences in microscopic structure, cell differentiation and pigment synthesis; however, associated proteomic differences are unclear. LE and UE can be easily sampled as single-layer-cell tissues for comparative proteomic analysis. In this study, a proteomic approach based on 2-DE and mass spectrometry (MS) was applied to compare LE and UE of fleshy scales from yellow and red onions. We identified 47 differential abundant protein spots (representing 31 unique proteins) between LE and UE in red and yellow onions. These proteins are mainly involved in pigment synthesis, stress response, and cell division. Particularly, the differentially accumulated chalcone-flavanone isomerase and flavone O-methyltransferase 1-like in LE may result in the differences in the onion scale color between red and yellow onions. Moreover, stress-related proteins abundantly accumulated in both LE and UE. In addition, the differential accumulation of UDP-arabinopyranose mutase 1-like protein and β-1,3-glucanase in the LE may be related to the different cell sizes between LE and UE of the two types of onion. The data derived from this study provides new insight into the differences in differentiation and developmental processes between onion epidermises. This study may also make a contribution to onion breeding, such as improving resistances and changing colors.

A review of anti-inflammatory, antioxidant, and immunomodulatory effects of Allium cepa and its main constituents

“…Also, differences in UDP-arabinopyranose mutase 1-like protein and β-1,3-glucanase in the LE, may be related to the differences in cell sizes in LE and UE of red and yellow onions (Wu et al. 2016 ). It was also shown that onions contain allylsulfides and flavonoids including quercetin which exert antioxidative activities and could reduce hepatocytes apoptosis; also, onion contains steroid saponins and sapogenins, and β-chlorogenin which is a characteristic steroid sapogenin.…”

Omics approaches inAlliumresearch: Progress and way ahead

“…2-DE and MS approaches identified 47 differential abundant protein spots between lower and upper epidermis of scales in red and yellow onions; among these, 31 were reported to be unique proteins. These differential proteins were involved in flavonoid synthesis, response to stress, and cell division ( Wu et al, 2016 ) . While studying gametogenesis and sterility in garlic, significant differences were observed in the 2-DE profile between sterile and fertile genotypes.…”

On the Promising Role of Enzyme Activity Assay in Interpreting Comparative Proteomic Data in Plants

“…[24] Scale epidermises of from yellow and red onion bulbs The abundance and enzymatic activity of β-1,3-glucanase were all higher in upper epidermis in both onions. [3] Imbibed sunflower seeds at 20 or 10°C 2DE-based; LC-MS/MS 105 DAPs, including 49 enzymes Ten enzymes by ABBP method Low concordance between enzyme abundance and activity. GAPDH, PGK, MDH, and AlaT increased in abundance at 20°C but showed low activity compared to 10°C.…”

“…The interpretation and validation of proteomic data has always been a common concern in the proteomics community. [2][3][4] Once DAPs are identified in comparative proteomics, it is essential to confirm the change in their abundance, and their role in the biological process under scrutiny. Eukaryotic proteins generally have multiple independent functions, especially as enzymes.…”