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

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.

DNA Damage Inducible Protein 1 is Involved in Cold Adaption of Harvested Cucumber Fruit

“…Therefore, the fruits are required to quickly respond to any environmental changes in order to stay physiologically healthy and genetically stable. Harvested fruits continue as living organs and play a critical role in protecting seeds inside (Wang et al, 2018a). Therefore, the fruits must have the capacity to initiate defenses against environmental stresses well before the onset of the real stress.…”

“…To further confirm the involvement of H 2 O 2 in PsCAinduced defense against chilling stresses, we analyzed the expression of six more defense genes related to chilling resistance: ASR1, GSH-Px, Prd-2B, SOD(Cu-Zn), L-APX6 and POD (Yoshimura et al, 2004;Xia et al, 2017;Wang et al, 2018a). The results showed DPI application before cold acclimation strongly downregulated all the six genes compared to PsCA treatment alone ( Figure S6).…”

“…We previously demonstrated that cold acclimation enhances chilling tolerance in cucumber fruit through the activation of antioxidant systems (Wang and Zhu, 2017;Wang et al, 2018b). Using proteomic analysis, we demonstrated that cold acclimation significantly increased CsDDI1 accumulation in cucumber (Wang et al, 2018a). However, it is not clear whether CsDDI1 plays a role in initiating cold acclimation.…”

“…The fusion constructs and control vector were electroporated into Agrobacterium tumefaciens strain GV3101 using Gene PulserXcellTM Electroporation Systems (Bio-Rad, USA) and then transformed into tobacco (Nicotiana benthamiana) leaf using the infiltration method. GFP fluorescence in tobacco leaf was observed 48 h after transfection using a fluorescence microscope (Zeiss Axioskop 2 Plus) (Wang et al, 2018a).…”

“…One of the most challenging environmental stresses that a plant faces is chilling during its development. Fruits, in particular, either as reproductive organs (Valenzuela et al, 2017) or as commercial products (Wang et al, 2018a) are susceptible to chilling injury because of the large water content in their tissues. Therefore, chilling injury, which is usually caused by suboptimal non-freezing low temperature, is one of the leading factors that affects fruit quality and seed development.…”