Proteomic Analysis of Differentially Accumulated Proteins in Cucumber (Cucumis sativus) Fruit Peel in Response to Pre-storage Cold Acclimation.

Bin Wang,Fei Shen,Shijiang Zhu

doi:10.3389/fpls.2017.02167

Abstract

Harvested fruits are still living organs and respond to environmental stimuli. Low temperature storage is effective in extending life of harvested fruit, but it may also cause chilling injury. Cold acclimation has been shown to induce chilling tolerance in plants, but what proteomic changes caused by cold acclimation are related to defense against chilling stress remains largely unclear. Here, 3 d of pre-storage cold acclimation (PsCA) at 10°C reduced chilling injury and secondary disease severity in cucumber stored at 5°C by 51 and 94%, respectively, compared with the control which was directly stored at 5°C. Proteomic analysis of cucumber peel identified 21 significant differentially-accumulated proteins (SDAPs) right after PsCA treatment and 23 after the following cold storage (PsCA+CS). These proteins are mainly related to stress response and defense (SRD), energy metabolism, protein metabolism, signal transduction, primary metabolism, and transcription. The SRD proteins, which made up 37% of the 21 and 47% of the 23, respectively, represented the largest class of SDAPs, and all but one protein were up-regulated, suggesting accumulation of proteins involved in defense response is central feature of proteomic profile changes brought about by PsCA. In fruit just after PsCA treatment, the identified SDAPs are related to responses to various stresses, including chilling, salt stress, dehydration, fungi, bacteria, insects, and DNA damage. However, after prolonged cold storage, the targeted proteins in acclimated fruit were narrowed down in scope to those involved in defense against chilling and pathogens. The change patterns at the transcription level of the majority of the up-regulated differentially-accumulated proteins were highly consistent with those at protein level. Taken all, the results suggest that the short-time cold acclimation initiated comprehensive defense responses in cucumber fruit at first, while the long term storage thereafter altered the responses more specifically to chilling. These findings add to the understanding of plants' molecular responses to cold acclimation.

Highlights

Harvested fruit, removed from the supporting tissues, continues as a living organ responsive to environmental stimuli
Chilling injury leads to loss of cell integrity of the peel, causing electrolyte leakage (EL), which can be used as a quantitative indicator for chilling injury (Cao et al, 2012; Liu et al, 2016)
The maximal PSII quantum yield (Fv/Fm) is a chlorophyll fluorescence parameter. This ratio reflects the maximum potential quantum efficiency of Photosystem II and a decline in Fv/Fm is related a loss of photosynthetic activity in fruit during cold storage (Huang et al, 2012; Li et al, 2015), and Fv/Fm has been widely used for evaluating cold tolerance in plants (Xia et al, 2009; Li et al, 2015; Wang et al, 2016)

Summary

Introduction

Removed from the supporting tissues, continues as a living organ responsive to environmental stimuli. Chilling injury in fruit would endanger the development of seeds To combat this stress and make sure that seeds are properly matured, the fruit has evolved the ability to get acclimated at the cue of chilling temperature, a process referred to as cold acclimation, by which a plant develops cold tolerance after an initial exposure to a critical temperature (Thomashow, 1999; Wang and Zhu, 2017). Many studies have been reported on plants’ molecular responses to cold acclimation, which have especially addressed the role of CBF (CRT/DRE-binding factor) pathway in acquisition of cold tolerance. The increase in freezing tolerance that occurs with cold acclimation is only partially dependent on the CBF-CRT/DRE regulatory module (Park et al, 2015). It is necessary to investigate what happens to proteomic profile under cold-acclimated condition, since proteins are the major class of functional molecules in plant cells (Renaut et al, 2006; Chen et al, 2015)

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