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 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.

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 (Eriobotrya japonica Lindl.) is a subtropical evergreen fruit tree that accumulates abundant bioactive triterpene compounds with diverse pharmaceutical activities. Its leaves have been used in traditional Chinese medicine for over 1000 years. Methyl jasmonate (MeJA) is a conserved elicitor that stimulates plant secondary metabolism. However, the regulatory mechanisms of terpenoid biosynthesis after MeJA treatment in loquat callus remain largely unknown. In this study, we employed an integrated targeted metabolomic and transcriptomic approach to investigate the effect of exogenous MeJA on terpenoid biosynthesis in loquat callus. In total, 131 terpenoid compounds were detected, including 112 triterpenes, six triterpene saponins, seven diterpenoids, three sesquiterpenoids and three monoterpenoids. After MeJA treatment, a total of 55 and 33 differential metabolites (DEMs) were identified at 24 h and 48 h, respectively. Most DEMs were triterpene compounds, displaying increased accumulation. Among them, ursolic acid showed the highest accumulation at 24 h, and betulinic acid was most abundant at 48 h. Meanwhile, transcriptome analysis showed significant upregulation of terpenoid biosynthesis genes, including EjFPSs, EjSQEs, EjOSC2 and EjCYP716A2, as well as genes related to jasmonic acid (JA)-mediated signaling and JA-responsive genes in loquat callus treated with MeJA. Overall, these results provide a deeper understanding of the mechanism of terpenoid accumulation in loquat callus induced by MeJA and establish a theoretical basis for utilizing plant cell culture techniques to achieve production of the valuable terpenoid metabolites that are applied in the functional food and pharmacological industries.