Comparative analysis of primary metabolites and transcriptome changes between ungrafted and pumpkin-grafted watermelon during fruit development

Ali Aslam; Shengjie Zhao; Muhammad Azam; Xuqiang Lu; Nan He; Bingbing Li; Junling Dou; Hongju Zhu; Wenge Liu

doi:10.7717/peerj.8259

Comparative analysis of primary metabolites and transcriptome changes between ungrafted and pumpkin-grafted watermelon during fruit development

PeerJ. 2020 Jan 6:8:e8259. doi: 10.7717/peerj.8259. eCollection 2020.

Authors

Ali Aslam¹, Shengjie Zhao¹, Muhammad Azam², Xuqiang Lu¹, Nan He¹, Bingbing Li¹, Junling Dou¹, Hongju Zhu¹, Wenge Liu¹

Affiliations

¹ Zhengzhou Fruit Research Institute, Chinese Academy of Agricultural Sciences, Zhengzhou, Henan, China.
² Institute of Horticultural Sciences, University of Agriculture, Faisalabad, Punjab, Pakistan.

Abstract

Grafting has been reported as a factor that influences fruit quality. However, a comprehensive study of the metabolic profile related to fruit quality and the underlying molecular mechanism in grafted watermelon has not been carried out. Metabolomics and transcriptome analysis were performed on both pumpkin-grafted watermelon and ungrafted watermelon at different developmental stages. In total, 56 primary metabolites were identified with either high or low abundance between ungrafted and pumpkin-grafted watermelon. The results indicated that ornithine, arginine, lysine (amino acids), glucose, sucrose, glucosamine (sugars), malic acid, fumaric acid and succinic acid (organic acids) were among the dominant metabolites influencing fruit quality. Additionally, comparative RNA sequence analysis on grafted and ungrafted watermelon yielded 729, 174, 128 and 356 differentially expressed genes at 10, 18, 26 and 34 days after pollination (DAP), respectively. Functional annotations of these genes indicated that grafting significantly altered the biological and metabolic processes related to fruit quality. Our comparative metabolomics and transcriptome analysis revealed that FBA2, FK, SuSy, SPS, IAI, AI and sugar transporter gene (SWT3b) might play a central role in the accumulation of glucose and sucrose, whereas higher malic acid content was attributed to high down regulation of ALMT13 and ALMT8 in pumpkin-grafted watermelon. Changes in the ornithine, glutamine, alanine, tyrosine, valine, asparagine, phenylalanine, arginine and tryptophan contents were consistent with the transcript level of their metabolic genes such as NAOD, GS, AGT, TaT, aDH1, OGDH, aDC, 4CL 1, PaL, CaT and two nitrate transporter genes (NRT1) in pumpkin-grafted watermelon. This study provides the basis for understanding the graft-responsive changes in the metabolic profile and regulatory mechanism related to fruit quality.

Keywords: Amino acid; Citrullus lanatus; Grafting; Metabolism; Organic acids; Sugar; Transcriptome; qRT-PCR.

Grants and funding

This research was supported by the Agricultural Science and Technology Innovation Program (CAAS-ASTIP-2016-ZFRI-07), the National Key R&D Program of China (2018YFD0100704), the China Agriculture Research System (CARS-25-03) and the National Nature Science Foundation of China (31672178 and 31471893). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.