Abstract
Plant grafting has been practiced widely in horticulture and proved as a useful tool in science. However, the mechanisms of graft healing or graft incompatibility remain poorly understood. In this study, Litchi chinensis cv. ‘Jingganghongnuo’ homograft (‘J/J’) and ‘Jingganghongnuo’/‘zhuangyuanhong’ heterograft (‘J/Z’) as compatible and incompatible combination, respectively, was used to study transcriptional changes between incompatible and compatible graft during graft union formation. Anatomical observation indicated that three stages (2 h, 14 d and 21 d after grafting) were critical for graft union formation and selected for high-throughput sequencing. Results indicated 6060 DEGs were differentially expressed in the compatible combination and 5267 DEGs exhibiting in the incompatible one. KEGG pathway enrichment analysis revealed that DEGs were involved in metabolism, wound response, phenylpropanoid biosynthesis and plant hormone signal transduction. The expression of 9 DEGs annotated in auxin pathway was up-regulated in compatible combination than that in incompatible combination. The IAA concentration confirmed that the IAA might promote the graft compatibility. In addition, 13 DEGs related to lignin biosynthesis were differentially expressed during graft healing process. Overall, our results provide abundant sequence resources for studying mechanisms underlying graft compatibility and establish a platform for further studies of litchi and other evergreen fruit trees.
Highlights
Grafting is an ancient asexual plant propagation technique that has been widely practiced in agriculture and horticulture
Zheng et al.[9] used cDNA-AFLP to examine the gene expression in hickory (Caryaca thayensis) during graft healing process, and the results indicated that the genes involved in indole-3-acetic acid (IAA) transport, cell cycle, signal transduction, and metabolism were differentially expressed
By comparing anatomical and transcriptional differences in compatible and incompatible grafts at three different developmental stages, we hypothesize that genes related to wound response, IAA and signal transduction pathway might play a key role in litchi grafting healing process
Summary
Grafting is an ancient asexual plant propagation technique that has been widely practiced in agriculture and horticulture. As a wound healing process for plants, graft union formation presumably requires considerable re-programming of gene expression, protein translation, and metabolism[8]. Graft union development and vascular reconnection in model plant Arabidopsis has been studied at the histological and transcriptional level[3, 10]. It is possible that the differentially expressed genes between compatible and incompatible graft combination revealed at transcriptome level could provide key information about the genes related to the vascular connections between the rootstock and scion. By comparing anatomical and transcriptional differences in compatible and incompatible grafts at three different developmental stages, we hypothesize that genes related to wound response, IAA and signal transduction pathway might play a key role in litchi grafting healing process. This study would provide useful information for revealing the mechanism of graft healing in plant
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