Tomato fruit ripening is accompanied by carotenoid accumulation and color changes. To elucidate the regulatory mechanisms underlying carotenoid synthesis during fruit ripening, a combined transcriptomic and metabolomic analysis was conducted on red-fruited tomato (WP190) and orange-fruited tomato (ZH108). A total of twenty-nine (29) different carotenoid compounds were identified in tomato fruits at six different stages. The abundance of the majority of the carotenoids was enhanced significantly with fruit ripening, with higher levels of lycopene; (E/Z)-lycopene; and α-, β- and γ-carotenoids detected in the fruits of WP190 at 50 and 60 days post anthesis (DPA). Transcriptome analysis revealed that the fruits of two varieties exhibited the highest number of differentially expressed genes (DEGs) at 50 DPA, and a module of co-expressed genes related to the fruit carotenoid content was established by WGCNA. qRT-PCR analysis validated the transcriptome result with a significantly elevated transcript level of lycopene biosynthesis genes (including SlPSY2, SlZCIS, SlPDS, SlZDS and SlCRTSO2) observed in WP190 at 50 DPA in comparison to ZH108. In addition, during the ripening process, the expression of ethylene biosynthesis (SlACSs and SlACOs) and signaling (SlEIN3 and SlERF1) genes was also increased, and these mechanisms may regulate carotenoid accumulation and fruit ripening in tomato. Differential expression of several key genes in the fruit of two tomato varieties at different stages regulates the accumulation of carotenoids and leads to differences in color between the two varieties of tomato. The results of this study provide a comprehensive understanding of carotenoid accumulation and ethylene biosynthesis and signal transduction pathway regulatory mechanisms during tomato fruit development.

Alfin-like (AL) transcription factors are a family of plant-specific genes with a PHD-finger-like structural domain at the C-terminus and a DUF3594 structural domain at the N-terminus that play important roles in plant development and stress response. In the present study, genome-wide identification and analysis were performed of the AL protein family in cultivated tomato (Solanum lycopersicum) and three wild relatives (S. pennellii, S. pimpinellifolium, and S. lycopersicoides) to evaluate their response to different abiotic stresses. A total of 39 ALs were identified and classified into four groups and based on phylogenetic tree and evolutionary analysis were shown to have formed prior to the differentiation of monocotyledons and dicots. Moreover, cis-acting element analysis revealed that various phytohormone response and abiotic stress response elements were highly existed in tomato. In addition, further analysis of the SlAL3 gene revealed that its expression was induced by drought and salt stresses and localized to the nucleus. In conclusion, our findings concerning AL genes provide useful information for further studies on their functions and regulatory mechanisms and provide theoretical references for studying AL gene response to abiotic stresses in plants.