Transcriptomic and Physiological Analysis Reveal That α-Linolenic Acid Biosynthesis Responds to Early Chilling Tolerance in Pumpkin Rootstock Varieties

Abstract

Climate changes especially chilling stress affects cucurbit crops during winter seasonal production. Grafting to pumpkin rootstocks is widely used to improve the vigor of cucurbits, especially cucumber (Cucumis sativus L.) plants, in the face of chilling stress. In our study, multi-disciplinary aspect approaches were used to investigate growth changes of pumpkin under chilling stress. Firstly, the morphological and physiological characteristics of 14 pumpkin (Cucurbita moschata) varieties following different periods of chilling stress was analyzed by using physiological means. Mathematical results of principal component analysis (PCA) with chlorophyll-a, chlorophyll-b, carotenoid contents, chilling injury index and relative electrolyte permeability indicated that relative electrolyte permeability as the primary judgment index was best associated with the comparison of chilling tolerance in pumpkin rootstock varieties. Then, transcriptomic and DCMU (Diuron) application and chlorophyll fluorescence examination analysis of pumpkin leaves revealed that 390 Cucurbita moschata differentially expressed genes (CmoDEGs) that affect photosynthesis were upregulated in leaves. 127 CmoDEGs both in leaves and roots were enriched for genes involved in unsaturated fatty acid metabolism, suggesting that plasma membrane lipids are involved in chilling perception. The results of increased composition of unsaturated fatty acid in leaves and qRT-PCR analysis of relative mRNA abundance confirmed that α-linolenic acid biosynthesis was responding to pumpkin chilling tolerance. The integration of physiological, mathematical bioinformatical and biological analysis results contributes to our understanding of the molecular mechanisms underlying chilling tolerance and its improvement in cucumber grafted on pumpkin rootstocks. It provided an important theoretical basis and reference for further understanding on the impact of climate change on plant physiological changes.

Rootstock–scion exchanging mRNAs participate in the pathways of amino acid and fatty acid metabolism in cucumber under early chilling stress

“…As is well known, when plants are subjected to external cold stress, the carbohydrate assimilation rate will be reduced, accompanied by reduced efficiency of the calvin cycle [ 53 ] and decreased fluidity of the plasma membrane, which is easily destroyed [ 54 – 56 ], resulting in an increase in membrane permeability, relative electrolyte leakage, and intracellular ion imbalance [ 57 ]. In this respect, our results indicated that lipid metabolism is the first player in the chilling response in Csa/Cmo and Cmo/Csa heterografts compared with Csa/Csa homografts [ 29 , 58 – 62 ].…”

“…Chilling treatment was performed as described in a previous study [ 29 ]. Briefly, at 7 days after grafting, around 100 seedlings of each graft combination were transferred into a light incubator under a chilling stress condition (4°C).…”

“…The contents of chlorophyll a, chlorophyll b, carotenoids, and MDA, and REP, were determined referring to previous study [ 29 ]. Three to five individual seedlings and 7–10 leaf disks per leaf for each graft combination were harvested into three replicate pools at each chilling treatment time point for further analysis.…”

“…Moreover, metabolome profiling analysis, which is widely used to investigate important agricultural traits such as flavor, yield, biomass, and nutritional quality, confirmed that grafting significantly increases the contents of primary metabolites such as sugar, organic acids, and amino acids in cucumber [ 26 ] and watermelon fruits [ 27 ]. The most interesting phenomenon is that the acquisition of chilling tolerance in grafted crops depends on the tolerance capacity of both rootstock and scion, and the different chilling tolerances of different combinations of rootstocks and scions [ 28 , 29 ]. Therefore, there exists signaling communication in response to chilling tolerance between scion and rootstock.…”

Grafting Watermelon Onto Pumpkin Increases Chilling Tolerance by Up Regulating Arginine Decarboxylase to Increase Putrescine Biosynthesis

“…Watermelon ( Citrullus lanatus ) is an important horticultural crop belonging to the Cucurbitaceae family and cultivated worldwide. Grafting is widely used in horticulture production to enhance abiotic/biotic stress resistance, promote water and fertilizer absorption, increase yield, and improve fruit quality ( Lee et al, 2010 ; Schwarz et al, 2010 ; Migicovsky et al, 2019 ; Liu et al, 2021 ). Our previous research indicated that arginine biosynthesis contributes to pumpkin rootstock-induced chilling tolerance ( Shi et al, 2019 ).…”