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.

Phospholipase Ds (PLDs) are important phospholipid hydrolases in plants that play crucial roles in the regulation of plant growth, development, and stress tolerance. In this study, 14 PLD genes were identified in the tomato genome and were localized on eight chromosomes, and one tandem-duplicated gene pair was identified. According to a phylogenetic analysis, the genes were categorized into four subtypes: SlPLDα, β, and δ belonged to the C2-PLD subfamily, while SlPLDζ belonged to the PXPH-PLD subfamily. The gene structure and protein physicochemical properties were highly conserved within the same subtype. The promoter of all the SlPLD genes contained hormone-, light-, and stress-responsive cis-acting regulatory elements, but no significant correlation between the number, distribution, and type of cis-acting elements was observed among the members of the same subtype. Transcriptome data showed that the expression of the SlPLD genes was different in multiple tissues. A quantitative RT-PCR analysis revealed that the SlPLD genes responded positively to cold, salt, drought, and abscisic acid treatments, particularly to salt stress. Different expression patterns were observed for different genes under the same stress, and for the same gene under different stresses. The results provide important insights into the functions of SlPLD genes and lay a foundation for further studies of the response of SlPLD genes to abiotic stresses.

Tomato yellow leaf curl disease (TYLCD) significantly affects tomato yield. The jasmonic acid (JA) pathway is crucial in the defence response of plants; however, its role in plant resistance to TYLCD remains undefined. In production, CCC (chlorocholine chloride) is often used to cultivate strong seedlings to enhance seedling vitality and improve stress resistance. However, the mechanism through which CCC enhances disease resistance in tomatoes remains unclear. In this study, tomato seedlings were exogenously sprayed with 300 mg/L CCC before and after inoculation with tomato yellow leaf curl virus (TYLCV). The results indicated that no significant tomato yellow virus disease phenotype was observed in tomato seedlings after spraying with CCC and subsequent inoculation with the virus. Spraying CCC on seedlings inoculated with the virus and exhibiting typical phenotypes can significantly alleviate the yellowing and curling symptoms of new leaves and improve photosynthesis-related indicators in tomato plants. The detection of virus copy numbers within the plants revealed that the virus copy numbers in plants treated with CCC were significantly lower than those in the control group. Transcriptomic analysis revealed that, after spraying CCC, the key enzyme genes AOS2 and AOC in the JA synthesis pathway in tomatoes were significantly upregulated, whereas the expressions of JAZ2 and MYC2 genes, which negatively regulate JA synthesis, were significantly downregulated. In the stable state, JAZ proteins interact with MYC2 and inhibit its transcriptional activity of MYC2. Tomatoes overexpressing MYC2 and JAZ2 exhibit a significant decrease in TYLCD resistance. These results indicated that exogenous spraying CCC affected the expression of genes such as MYC2 and JAZ2, and then regulated JA pathway, increased the endogenous JA content in plants, and enhanced the disease resistance of tomato plants to TYLCD. This study provides a scientific reference for effectively preventing and controlling TYLCD in tomato production and reducing the influence of TYLCD on tomato yield and quality.