Eriobotrya is an evergreen fruit tree native to South-West China and adjacent countries. There are more than 26 loquat species known in this genus, while E. japonica is the only species yet domesticated to produce fresh fruits from late spring to early summer. Fruits of cultivated loquat are usually orange colored, in contrast to the red color of fruits of wild E. henryi (EH). However, the mechanisms of fruit pigment formation during loquat evolution are yet to be elucidated. To understand these, targeted carotenoid and anthocyanin metabolomics as well as transcriptomics analyses were carried out in this study. The results showed that β-carotene, violaxanthin palmitate and rubixanthin laurate, totally accounted for over 60% of the colored carotenoids, were the major carotenoids in peel of the orange colored ‘Jiefangzhong’ (JFZ) fruits. Total carotenoids content in JFZ is about 10 times to that of EH, and the expression levels of PSY, ZDS and ZEP in JFZ were 10.69 to 23.26 folds to that in EH at ripen stage. Cyanidin-3-O-galactoside and pelargonidin-3-O-galactoside were the predominant anthocyanins enriched in EH peel. On the contrary, both of them were almost undetectable in JFZ, and the transcript levels of F3H, F3’H, ANS, CHS and CHI in EH were 4.39 to 73.12 folds higher than that in JFZ during fruit pigmentation. In summary, abundant carotenoid deposition in JFZ peel is well correlated with the strong expression of PSY, ZDS and ZEP, while the accumulation of anthocyanin metabolites in EH peel is tightly associated with the notably upregulated expressions of F3H, F3’H, ANS, CHS and CHI. This study was the first to demonstrate the metabolic background of how fruit pigmentations evolved from wild to cultivated loquat species, and provided gene targets for further breeding of more colorful loquat fruits via manipulation of carotenoids and anthocyanin biosynthesis.

Eriobotrya japonica (loquat) is an evergreen fruit tree of the apple tribe in Rosaceae with high edible and medicinal value. The yield and quality of loquat fruits are significantly influenced by environmental stress, particularly heat stress during fruit ripening. In this study, thirty EjHSFs were identified in the loquat genome. Twenty-nine EjHSFs were unevenly distributed across sixteen chromosomes, except Chr-6. A synteny analysis revealed that twenty-six EjHSF genes had undergone duplication events. Twenty-nine EjHSF genes were found to be in sync with HSF in apples while also diverging with other Rosaceae species. A phylogenetic analysis revealed that EjHSFs could be divided into three categories, including eighteen EjHSF-A, ten EjHSF-B, and two EjHSF-C. Twenty-nine members of the EjHSF family showed high homology to those of Malus domestica and Gillenia trifoliate. A promoter analysis retrieved thirty-three CAREs that were functionally relevant and connected to the expression of HSFs. Among these, the promoters of twenty-three EjHSF genes possessed at least one STRE element that could be activated by heat shock. Eleven of these EjHSFs were highly expressed in loquat tissues, namely EjHSF-B4a, EjHSF-A4a, EjHSF-A4d, and EjHSF-C1a in roots; EjHSF-B4b in roots and inflorescence; EjHSF-C1b in stems and roots; EjHSF-A2a in three tissues; EjHSF-A8b in four tissues; and EjHSF-A4c, EjHSF-B1a, and EjHSF-B2b in six tissues. Moreover, fifteen EjHSFs were differentially expressed (eleven upregulated and four downregulated) in fruits under heat stress treatment in the color-changing period. Among them, EjHSF-A2a and EjHSF-A2b upregulated transcriptional abundance over 300 times after heat treatment; EjHSF-B2b consistently displayed an increasing trend over time; and EjHSF-B1a was significantly downregulated. Hence, these results suggest that EjHSFs take part in loquat tissue development and may be involved in the fruit’s heat stress response. These findings enhance the understanding of EjHSFs’ role within loquats and the heat stress response of its fruit and provide target genes for heat stress improvement.

Loquat fruits from the apple tribe of Rosaceae ripen from late spring to early summer, when most fresh fruits are out of season. Compared with the orange-fleshed varieties, the white-fleshed varieties are usually preferentially chosen by consumers for a more favorable flavor. Though the breeding of white-fleshed cultivars with large fruit size greatly promoted the development of loquat production, the mechanisms of how fruits with lighter pigments are generated and how fruit flavor changes following flesh color shifting remain to be elucidated. Pigment measurements indicated carotenoids as the dominant pigment underlying the change in flesh color changing. Genotyping and haplotyping of 807 loquat accessions revealed that the rise of PSY2A^d-PSY2A^d genotype blocks carotenoids accumulation and confers to white flesh color of loquat fruit. Analysis of widely targeted metabolomes on 18 representative cultivars identified 1420 metabolites, with 223 differentially accumulated metabolites between the two groups. Further metabolite comparison demonstrated that low levels of bitter or astringent compounds, such as flavonoids, lignans and coumarins, phenolic acids, nucleotides, alkaloids, and terpenoids, may confer to a refreshing flavor of white-fleshed fruits. Furthermore, 18 metabolic biomarkers were identified by machine learning to distinguish fruits with diverse flesh colors. This work gives insights into the understanding of how fruit color variation associated with flavor and also promotes white-fleshed loquat breeding by genus-wide genotyping.

γ-aminobutyric acid (GABA) is a four-carbon non-protein amino acid, with many regulatory effects in humans. It aids in regulating blood glucose levels and pressure and is widely recognized for its ability to promote cognitive balance through the alleviation of stress and improvements in sleep quality. The GABA content of longan pulp is higher than that of many other fruits and vegetables; however, much is still unknown about GABA’s biosynthesis in longan. In this study, we found that the GABA content of ‘Baoshi No. 1’ (BS1) pulp was significantly higher than that of ‘Chunxiang’ (CX) pulp. The GAD activity was higher in BS1 pulp than CX pulp, while there was no significant difference in the GABA-T activity. Additionally, five GAD genes were identified in longan, and an analysis of their transcriptional levels showed that only the expression level of DlGAD3 corresponded to the GABA content and GAD activity. DlGAD3 was localized in the cytoplasm, and its transient overexpression promoted an increase in the GABA content in Nicotiana benthamiana leaves. Overall, our results show that DlGAD3 is able to promote the accumulation of GABA and may play a major role in its biosynthesis in longan pulp.

Loquat is an evergreen fruit crop which blooms from autumn–winter, and supports human beings with juicy fruit from late spring to early summer. However, the most traditional cultivars of this crop produce small fruit and bear a much lower yield than its relatives like apple, pear and peach. Large-size cultivars have long been a cherished aim of breeders for improving the production yield of loquat. Agronomic practices like panicle thinning, fruit thinning, growth regulator application, fertilization and so on are easier and more accessible ways for growers to produce large-size loquat fruit on existing production trees. Here, we develop a novel pruning method with an annual double back-cut, which provides vigorous shoot with more leaves and thicker branches for bearing much larger loquat fruit. Cellular observation determined that the vigorous shoot training method motivated cell division to produce larger loquat fruit, and that most of these cell layers were proliferated before the appearance of flower blossoms. Gene expression data of four development stages showed that EjFWL1 and EjFWL2 were notably downregulated in flower buds of the vigorously pruned tree. The data here further confirmed that the cell division capacity during flower development greatly influenced both the flower and fruit size of loquat. More importantly, we developed a novel pruning method to inhibit cell division repressors, promote cell proliferation and enlarge fruit size in loquat.

Pyrops candelaria is one of the common pests of fruit trees, but the research on the pathogenic microorganisms it may carry is very limited. Therefore, it is essential to reveal the pathogenic microbes it carries and their potential hazards. This study found a new virus from the transcriptome of P. candelaria, which was first reported in P. candelaria and named PyCaV (Pyrops candelaria associated virus). RACE and bioinformatics assay revealed that the full length of PyCaV is 10,855 bp with the polyA tail, containing a single open-reading frame (ORF) encoding a polyprotein consisting of 3171 amino acid (aa). The virus has a typical iflavirus structure, including two rhv domains, an RNA helicase domain (HEL), a 3C cysteine protease domain (Pro), and an RNA–dependent RNA polymerase domain (RdRp). Further phylogenetic analysis revealed that this virus belongs to family Iflaviridae and sequence alignments analysis suggested PyCaV is a new member in an unassigned genus of family Iflaviridae. Further in-depth analysis of the virus infection showed that PyCaV is distributed throughout the whole P. candelaria, including its head, chest, and abdomen, but more PyCaV was identified in the chest. The distribution of PyCaV in different parts of P. candelaria was further explored, which showed that more PyCaV was detected in its piercing–sucking mouthparts and chest viscera. Statistical analysis showed that the PyCaV infection was affected by time and location.