Na Li

The cuticular wax of ‘Hupingzao,’ an important economic crop in China, not only constitutes a key factor in determining the appearance quality and gloss of the fruit but also plays a vital role in regulating water evaporation and resisting biotic and abiotic stresses. In this study, ‘Hupingzao’ fruit produced during the white−ripe (WR) and full−red (FR) periods were used as study materials. The key genes and components of wax development were screened using a combination of transcriptomics and metabolomics. Enrichment analysis was performed on the differential genes and metabolites, and the fatty acid biosynthesis and elongation pathways were selected for further study. A series of key candidate genes in the de novo synthesis, elongation, and subsequent modification pathways of fatty acids were identified, such as acetyl−CoA carboxylase (ACCase), fabF (β−Ketoacyl−ACP Synthase II), and β−ketoacyl−CoA synthase (KCS). To further explore the mechanism of jujube wax biosynthesis, GC−MS (gas chromatography–mass spectrometry) was used to determine and analyze the content and composition of the wax after it was treated with gibberellin and paclobutrazol. The results showed that spraying the plants with GA₃ significantly upregulated the expression of genes involved in fatty acid de novo synthesis and elongation such as accC (Acetyl−CoA Carboxylase, Biotin Carboxylase Subunit), fabD (Malonyl−CoA:ACP Transacylase), fabG (β−Ketoacyl−ACP Reductase), fabI (Enoyl−ACP Reductase), ACSL (Long−chain Acyl−CoA Synthetase), and KCS and increased the content of dodecanoic acid, behenic acid, lignoceric acid, and hexacosanoic acid. These results suggest that the GA signal may participate in the upregulation of fatty acid synthesis. In this study, we systematically constructed a molecular map of wax fatty acid metabolism during the fruit development stage of the ‘Hupingzao’ variety, providing an important theoretical basis and candidate genes for future directional regulation of wax components via molecular breeding or cultivation measures.

This study investigated the phylogenetic relationships in the pear calcium-dependent protein kinase (CDPK) pan-gene family and elucidated its role in the resistance to scab disease caused by Venturia nashicola. By integrating data from eight genomic sets from five cultivated pear species, Pyrus bretschneideri, P. ussuriensis, P. sinkiangensis, P pyrifolia, and P. communis, along with P. betulifolia and interspecific hybrids, 63 PyCDPK family members were identified. Among these, P. communis possessed the highest number of CDPK genes, whereas P. bretschneiderilia had the fewest. These genes encode proteins ranging from 459 to 810 amino acids in length, and are predominantly localized to the cell membrane. Six genes, PyCDPK9, PyCDPK11, PyCDPK12, PyCDPK14, PyCDPK16, and PyCDPK19, were classified as core members of the pan-genome, and PyCDPK19 showed evidence of positive selection pressure. Clustering analysis and transcriptomic expression profiling of disease-resistance-related CDPKs identified PyCDPK19 as a key candidate associated with scab resistance. Promoter analysis revealed that the regulatory region of PyCDPK19 contains multiple cis-acting elements involved in defense responses and methyl jasmonate signaling. Transient overexpression of PyCDPK19 in tobacco leaves induced hypersensitive cell necrosis, accompanied by significant increases in hydrogen peroxide (H₂O₂) accumulation and malondialdehyde (MDA) content. Similarly, overexpression in pear fruit callus tissue followed by pathogen inoculation resulted in elevated levels of both H₂O₂ and MDA. Collectively, these findings indicate that PyCDPK19 mediates defense responses through the activation of the reactive oxygen species pathway in both tobacco and pear plants, providing a promising genetic target for enhancing scab resistance in pears.

Salicylic acid (SA) is known to be an efficient elicitor of secondary metabolism in plants. Arbutin, a characteristic phenolic glycoside found in ‘Yuluxiang’ pear (Pyrus bretschneideri Rehder × Pyrus sinkiangensis Yu), is widely used in lightening agents, in addition to cough, anti-inflammatory, and anti-microbial remedies, among other applications. However, research into the synthesis of arbutin in pear is limited. This study aimed to clarify the effect of exogenous SA on the arbutin content of pear using HPLC and investigate the mechanism for arbutin accumulation using RNA-Seq analysis. HPLC revealed that SA increased the arbutin contents of leaf, fruit, and callus in pear and demonstrated that the effect of SA is concentration and time dependent. RNA-Seq analysis of pear callus treated with or without SA revealed 380 differentially expressed genes (DEGs), 335 of which were up-regulated. According to a KEGG database analysis, the highest number of genes were annotated for phenylpropane biosynthesis. Overall, 21 DEGs were found to be involved in the synthesis of hydroquinone and UDP-glucose, which are substrates of arbutin synthesis. It is noteworthy that the expression levels of three up-regulated genes (Pbr006844.1, Pbr021064.1 and Pbr021069.1) related to hydroquinone glycosyltransferase were induced by SA and hydroquinone. Furthermore, transient overexpression of PbUGT72B1 (Pbr021069.1) increased the arbutin content in pear callus. These data explain the regulation of gene transcription associated with the promotive effect of SA on arbutin biosynthesis in pear, thus providing a theoretical foundation for enhancing the arbutin content of fruit through genetic engineering.

The membrane proteins of the magnesium transporter (MGT) family are essential to Mg homeostasis. However, there has not been a comprehensive study of MGT in pear. The 17 MGT that were renamed to PbMGT1–17 in this study were found in the pear genome database. Phylogenetically, PbMGT proteins were categorized into three groups, namely NIPA, MRS2, and CorA. The majority of PbMGT were hydrophobic proteins situated on the chloroplast, according to the characterization study. Members of the same group shared comparable conserved motifs and gene structure, as revealed by motif and exon/intron analysis. The application of gene ontology (GO) and cis-elements has demonstrated that PbMGT genes exhibit a high degree of sensitivity to stressors and take part in chloroplast development and Mg⁺ ion transport. It was discovered by tissue-specific expression analysis that PbMGT genes might have a role in the development of organs. The critical significance of PbMGT was shown through comprehensive expression in five pear cultivars at various fruit developmental stages. The PbMGT5 gene was significantly expressed throughout fruit development, suggesting a role in the setting and ripening processes of pear fruits. For the first time, our research brought attention to the function of PbMGT genes as they relate to fruit development. Our research is likely to serve as an incentive for the development of pear breeding initiatives in the future.

Real-time quantitative PCR (RT-qPCR) has become a widely used method for exploring plant gene expression level. The method requires using some stably expressed genes as a reference to accurately normalize the RT-qPCR data. However, under various stresses and hormone treatments, the levels of most reference genes vary. Environmental variations also influence their expression levels. The lack of validated, stably expressed reference genes can mislead the study of gene function in pears. “Huangguan” pears have recently become the focus of research on stress resistance mechanisms, such as high resistance. Therefore, the aim of this study was to select the optimal reference genes in Huangguan pears, and we analyzed the expression of the genes EF1α, ACT, SKD1, YLS8, UBQ, GAPDH, TUB, and WDP in a series of pear leaf sets under various stresses and hormone treatments. Using different statistical algorithms, we found that under various treatments, the WDP gene had more stable expression, ACT was the most stable under MeJA treatment, YLS8 was the most valuable reference gene under ABA hormone and heat stress conditions, and GAPDH showed worst results compared to other housekeeping genes, except under heat stress. These results will supply valuable and updated information for the selection of housekeeping genes in pears under biotic and abiotic stresses in the future.

The ECERIFERUM (CER) gene family plays an important role in wax biosynthesis. However, little is known about the CER gene family in jujube (Ziziphus jujuba Mill.). We identified 29 CER genes in the Z. jujuba genome and named them ZjCER1 to ZjCER29 according to their chromosomal locations. We then investigated the chemical characteristics, gene structures, and evolutionary relationships of these ZjCER genes. The genes were classified into three clades according to their phylogenetic relationship with Arabidopsis thaliana and Malus domestica. One pair of syntenic orthologous CER genes was matched between Z. jujuba and M. domestica. Analysis of conserved gene motifs revealed similar motifs within clades; 27 ZjCER genes had two or more introns. Twelve representative ZjCER genes showed different expression patterns in two Z. jujuba cultivars with contrasting cracking-resistant character. To further analyze the potential roles of ZjCER genes in response to various circumstances, we examined a 2.0 kb promoter region of the candidate ZjCER genes. All ZjCER genes except ZjCER28 shared a light-responsive element, and most shared hormone-related cis-elements. Our results provide rich resources for studying CER genes and potential clues for genetic improvement of jujube wax biosynthesis for improvement of cracking in Z. jujuba fruit.

Background: Jujube is a typical fruit tree species from China. ‘Muzao’, a cracking-susceptible cultivar, and ‘Linhuang No. 1’, a cracking-resistant cultivar, were selected in a previous study as contrasting research materials. Whole-genome resequencing and transcriptomic analysis of ‘Linhuang No. 1’ and ‘Muzao’ allowed the identification of differentially expressed genes with different gene structures between the two cultivars and could be helpful in explaining the differences and similarities between the two cultivars. Results: Resequencing identified 664,129 polymorphic variable sites between ‘Linhuang No. 1’ and ‘Muzao’. To determine the genetic relationship among ‘Linhuang No. 1’, ‘Muzao’ and the jujube genome reference cultivar ‘Dongzao’, the characteristic polymorphic variable sites were analysed by principal component analysis. The genetic relationship between ‘Linhuang No. 1’ and ‘Muzao’ was closer than that of either variety and ‘Dongzao’. Nineteen differentially expressed genes were identified by combining transcriptomic analysis with resequencing analysis. LOC107427052 (encoding a nitrite reductase) was identified by Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis for further study. The identified insertion was not in the domain region of the LOC107427052 gene coding sequence (CDS) region and was verified by the finding that the insertion did not affect translation of the protein. The LOC107427052 gene expression levels, nitrite reductase activities and nitrite contents of ‘Muzao’ were significantly higher than the corresponding values of ‘Linhuang No. 1’ at the young fruit stage. There was no significant difference in the quantity of the product of nitrite reductase, namely, ammonia, between the two cultivars. Conclusions: The present study was the first to explore the differences between different jujube cultivars (‘Linhuang No. 1’ and ‘Muzao’) by combining genome resequencing and transcriptomics. LOC107427052 (encoding a nitrite reductase) was characterized by KEGG enrichment analysis. The insertion in the CDS region of the LOC107427052 gene provides a new direction for the study of nitrogen metabolism in jujube. Our study has laid a foundation for the comparative analysis of nitrite metabolism between the jujube cultivars ‘Linhuang No. 1’ and ‘Muzao’.

BackgroundJujube is one of the characteristic fruit tree species in China. ‘Linhuang No. 1’, a cracking-resistant cultivar, and ‘Muzao’, a cracking-susceptible cultivar, were selected as materials by previous study. Whole-genome re-sequencing and transcriptome of ‘Linhuang No. 1’ and ‘Muzao’ allow the screening out of differently expressed genes with different gene structures between them. It could be helpful in explaining divergence/similarity between the two cultivars. ResultsThere are 664,129 mutation sites between ‘Linhuang No. 1’ and ‘Muzao’ by re-sequencing. To determine the genetic relationship of ‘Linhuang 1’, ‘Muzao’ and reference genome ‘Dongzao’, the characteristic mutation sites were analyzed by principal component analysis. The genetic relationship between ‘Linhuang No. 1’ and ‘Muzao’ was closer than that with ‘Dongzao’. 19 differentially expressed genes were screened by combining the transcriptomics with re-sequencing analysis. LOC107427052 (encoding nitrite reductase) was determined by KEGG enrichment analysis for further study. The large base insertion was not in the domain region of the LOC107427052 gene CDS region. As verified by the finding that the base insertion did not affect protein translation. LOC107427052 gene expression levels, the nitrite reductase activities and the nitrite content of ‘Muzao’ were significantly higher than those of ‘Linhuang No. 1’ at young fruit stage. There was no significant difference in the product ammonia of nitrite reductase between the two varieties. ConclusionsOur study has laid a foundation for the analysis of genetic information and the comparative nitrite metabolism of ‘Linhuang No. 1’ and ‘Muzao’.