De novo Comparative Transcriptome Analysis of Genes Differentially Expressed in the Scion of Homografted and Heterografted Tomato Seedlings

Tomato is an important vegetable crop grown worldwide. Grafting is an agricultural technique that is used to improve growth, yield, and resistance to diverse stresses in tomato production. Here, we examined the differences between the scion of heterografted (‘Provence’/‘Haomei’) and homografted (‘Provence’/‘Provence’) tomato seedlings. We observed anatomical changes during the graft-union healing process in heterografted and homografted tomato seedlings and conducted transcriptome analyses of the ‘Provence’ scion from both graft combinations. With the development of calli from both graft partners, the isolation layer became thinner at 16 d after grafting (DAG). Compared with that of homografts, the healing in heterografts was slightly delayed, but the graft union had completely healed at 21 DAG. In total, 858 significantly differentially expressed genes were detected between the transcriptomes of heterografts and homografts at 16 DAG. Functional pathways identified by GO and KEGG enrichment analyses were associated with primary and secondary metabolism, hormone signalling, transcription factor regulation, transport, and responses to stimuli. Many differentially expressed genes were involved in pathways associated with mitogen-activated protein kinase signalling, plant hormone signalling, and oxidative stress. A number of transcription factors were up-regulated in the scion of heterografted seedlings. The results provide a valuable resource for the elucidation of the molecular mechanisms, and candidate genes for functional analyses, of heterograft and homograft systems.