Abstract
Hickory (Carya cathayensis), a tree with high nutritional and economic value, is widely cultivated in China. Grafting greatly reduces the juvenile phase length and makes the large scale cultivation of hickory possible. To reveal the response mechanisms of this species to grafting, we employed a proteomics-based approach to identify differentially expressed proteins in the graft unions during the grafting process. Our study identified 3723 proteins, of which 2518 were quantified. A total of 710 differentially expressed proteins (DEPs) were quantified and these were involved in various molecular functional and biological processes. Among these DEPs, 341 were up-regulated and 369 were down-regulated at 7 days after grafting compared with the control. Four auxin-related proteins were down-regulated, which was in agreement with the transcription levels of their encoding genes. The Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed that the ‘Flavonoid biosynthesis’ pathway and ‘starch and sucrose metabolism’ were both significantly up-regulated. Interestingly, five flavonoid biosynthesis-related proteins, a flavanone 3-hyfroxylase, a cinnamate 4-hydroxylase, a dihydroflavonol-4-reductase, a chalcone synthase, and a chalcone isomerase, were significantly up-regulated. Further experiments verified a significant increase in the total flavonoid contents in scions, which suggests that graft union formation may activate flavonoid biosynthesis to increase the content of a series of downstream secondary metabolites. This comprehensive analysis provides fundamental information on the candidate proteins and secondary metabolism pathways involved in the grafting process for hickory.
Highlights
Hickory (Carya cathayensis), an important member of the Juglandaceae, is a popular and commercially available tree that is widely grown in Zhejiang Province, China
We identified the differentially expressed proteins (DEPs) during the process of grafting hickory by applying high-throughput quantitative proteomics and Tandem Mass Tag (TMT) isobaric labeling (Figure 1A)
The results revealed that the DEPs (7D/0D < 1/1.5) were most strongly associated with ‘starch and sucrose metabolism,’ and ‘carbon fixation in photosynthetic organisms’; the 7D/0D > 1.3 DEPs were most strongly involved in phenylpropanoid biosynthesis and terpenoid backbone biosynthesis; and the 7D/0D > 1.5 DEPs were associated with flavonoid biosynthesis (Figure 3B)
Summary
Hickory (Carya cathayensis), an important member of the Juglandaceae, is a popular and commercially available tree that is widely grown in Zhejiang Province, China. Comparative Proteomic Analysis of Hickory outside of cultivation, the long juvenile stage lasts for over 10 years before a hickory tree reaches maturity and reduces yields (Wang et al, 2014; Sima et al, 2015). Grafting an ancient technique plays an important role in plant propagation and improvement (Pina and Errea, 2005; Zheng et al, 2010). Grafting provides a good method for reducing the length of the juvenile stage during the cultivation of hickory (Zheng et al, 2010)
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