The loquat (Eriobotrya japonica L.) is a special evergreen tree, and its fruit is of high medical and health value as well as having stable market demand around the world. In recent years, research on the accumulation of nutrients in loquat fruit, such as carotenoids, flavonoids, and terpenoids, has become a hotspot. The SBP-box gene family encodes transcription factors involved in plant growth and development. However, there has been no report on the SBP-box gene family in the loquat genome and their functions in carotenoid biosynthesis and fruit ripening. In this study, we identified 28 EjSBP genes in the loquat genome, which were unevenly distributed on 12 chromosomes. We also systematically investigated the phylogenetic relationship, collinearity, gene structure, conserved motifs, and cis-elements of EjSBP proteins. Most EjSBP genes showed high expression in the root, stem, leaf, and inflorescence, while only five EjSBP genes were highly expressed in the fruit. Gene expression analysis revealed eight differentially expressed EjSBP genes between yellow- and white-fleshed fruits, suggesting that the EjSBP genes play important roles in loquat fruit development at the breaker stage. Notably, EjSBP01 and EjSBP19 exhibited completely opposite expression patterns between white- and yellow-fleshed fruits during fruit development, and showed a close relationship with SlCnr involved in carotenoid biosynthesis and fruit ripening, indicating that these two genes may participate in the synthesis and accumulation of carotenoids in loquat fruit. In summary, this study provides comprehensive information about the SBP-box gene family in the loquat, and identified two EjSBP genes as candidates involved in carotenoid synthesis and accumulation during loquat fruit development.

Previous studies indicated that extensive genetic variations could be generated due to polyploidy, which is considered to be closely associated with the manifestation of polyploid heterosis. Our previous studies confirmed that triploid loquats demonstrated significant heterosis, other than the ploidy effect, but the underlying mechanisms are largely unknown. This study aimed to overcome the narrow genetic distance of loquats, increase the genetic variation level of triploid loquats, and systematically illuminate the heterosis mechanisms of triploid loquats derived from two cross combinations. Here, inter-simple sequence repeats (ISSRs) and simple sequence repeats (SSRs) were adopted for evaluating the genetic diversity, and transcriptome sequencing (RNA-Seq) was performed to investigate gene expression as well as pathway changes in the triploids. We found that extensive genetic variations were produced during the formation of triploid loquats. The polymorphism ratios of ISSRs and SSRs were 43.75% and 19.32%, respectively, and almost all their markers had a PIC value higher than 0.5, suggesting that both ISSRs and SSRs could work well in loquat assisted breeding. Furthermore, our results revealed that by broadening the genetic distance between the parents, genetic variations in triploids could be promoted. Additionally, RNA-Seq results suggested that numerous genes differentially expressed between the triploids and parents were screened out. Moreover, KEGG analyses revealed that “photosynthetic efficiency” and “glyco-metabolism” were significantly changed in triploid loquats compared with the parents, which was consistent with the results of physiological indicator analyses, leaf micro-structure observations, and qRT-PCR validation. Collectively, our results suggested that extensive genetic variations occurred in the triploids and that the changes in the “photosynthetic efficiency” as well as “glyco-metabolism” of triploids might have further resulted in heterosis manifestation in the triploid loquats.

Blueberry fruit quality is characterized by multi-dimensional traits such as color, sugar-acid flavor, and volatile aroma. However, variations in progeny metabolites during seedling selection need further study. This research used the blueberry variety ‘Baldwin’ (BW) and its seedling offspring (BWSO) to compare fruit appearance, as well as sugar and acid components, anthocyanin monomers, and volatile metabolites. High-performance liquid chromatography was used to analyze anthocyanins, sugars, and acids, and gas chromatography–mass spectrometry was used to analyze volatile compounds. The results showed that, compared with BW, BWSO had a blacker skin and a lower L* value. Its total anthocyanin content increased by 35.90%, with delphinidin increasing the most (52.70%); component ratios were reconstructed. The main organic acids in BWSO decreased; titratable acid dropped by 29.82%, and the total soluble solids–acid ratio rose by 37.49%, indicating a good low-acid, high-sugar flavor. Forty-three differential volatile metabolites were found, and BWSO differed from BW in its green, fruity, and floral flavors. Notably, BWSO’s vitamin C (Vc) content decreased by 70.45% compared to BW, and Vc was negatively correlated with anthocyanin components. In conclusion, BWSO exhibits a black phenotype due to elevated total anthocyanins and restructured component ratios. Its low-acid trait yields better taste, but the antagonism between anthocyanin and Vc means balanced nutritional quality selection is crucial in dark-blueberry breeding. These findings offer new insights into the mechanism of color variation and provide a reference for balanced quality trait selection in seedling selection.