Liu Cong

Expansins are crucial cell wall-loosening proteins that play a vital role in various plant developmental processes, including fruit ripening and softening. However, a comprehensive genome-wide analysis of the expansin family in apple (Malus × domestica) and the specific functions of its members in postharvest fruit ripening remain to be explored. In this study, we identified 51 expansin genes in the apple genome and classified them into four subfamilies (EXPA, EXPB, EXLA, and EXLB). Cis-element analysis of the promoters of apple expansin genes showed that these promoters are rich in various hormone-responsive elements, including abscisic acid (ABA)-responsive elements (ABREs) and ethylene-responsive elements (EREs), suggesting potential hormonal regulation of expansin genes. Expression profiling identified six ripening-associated expansin genes. Among them, MdEXPA5, MdEXPA17, and MdEXPA23 were positively regulated by both ethylene and ABA, while being suppressed by the ethylene action inhibitor 1-MCP. Further functional characterization demonstrated that transient overexpression of MdEXPA17 accelerated fruit softening, skin yellowing, ethylene production, and increased total soluble solid (TSS) content. Conversely, silencing of MdEXPA17 significantly delayed these ripening processes. Our study provides a systematic overview of the apple expansin gene family and supports a role for MdEXPA17 in promoting postharvest fruit ripening and softening. These findings offer valuable insights into the molecular mechanisms of apple fruit ripening and provide potential targets for genetic improvement of fruit quality and shelf life.

Plant seed number depends on ovule number initiated within the carpels, and it serves as a primary factor shaping fruit yield. Pomegranate trees exhibit bisexual flowers and functional male flowers. Pomegranate have anatropous ovules which are bitegmic and crassinucellate. Bisexual flowers possess the fertile pistil, while functional male flowers have abnormally developed ovules, a small ovary with few chambers, and a short style. The formation of functional male flowers is due to abnormal and stagnant development of ovule integument. Ovule number directly determines the yield of pomegranate seeds. Recent studies have highlighted the molecular mechanisms through which ovule-related genes regulate pomegranate ovule development. Pomegranate PgCRC and PgINO genes positively regulate the increase in the number of ovules, and PgBEL1 to synergistically regulate seed development. PgAGL11 (the SEEDSTICK orthologous gene) promotes ovule development in transgenic Arabidopsis. PgSEP protein can bridge interactions among PgBEL1, PgSTK and PgAG, which regulate ovule development. At the level of post-transcriptional regulation, PgmiRNA167, PgmiRNA164 and PgmiRNA160 are differentially expressed during pomegranate flower development, and PgmiR166a interacts with its target genes to affect ovule development. This review summarizes the key regulators of ovule development and their molecular pathways, integrating these interactions into a model that describes pomegranate ovule development.

Ascorbate oxidases (AAOs) are key regulators of extracellular redox homeostasis and plant stress responses, but their roles in grapevine defense remain unclear. Here, we performed a genome-wide analysis and characterization of the AAO gene family in grapevine Vitis amurensis, identifying 10 VaAAO genes that are unevenly distributed across six chromosomes, with notable clustering on chromosome 7. Promoter analysis revealed multiple phytohormone- and stress-responsive cis-elements (e.g., ARE, STRE, and TCA-element) and transcription factor binding sites (e.g., MYC/MYB, and WRKY), suggesting involvement in redox- and stress-related signaling pathways. Analysis of previously published transcriptomic data under Botrytis cinerea infection identified VaAAO7 as a key pathogen-responsive gene. VaAAO7 was rapidly induced by H₂O₂, and its transient ectopic overexpression in susceptible V. vinifera ‘Red Globe’ leaves significantly reduced lesion development. Together, these results demonstrate that VaAAO7 functions as a positive regulator of B. cinerea resistance and highlight its potential for genetic engineering to enhance systemic defense and develop disease-resistant grapevine cultivars.

Apple replant disease (ARD) poses a major threat to global orchard productivity, yet its biological causes remain poorly understood. Although microbial dysbiosis in replant soils has been recognized as a major contributing factor, the specific pathogenic agents involved and the efficacy of synthetic microbial communities in mitigating ARD remain unclear. In this study, we integrated physiological, transcriptomic, metabolomic, and microbiome analyses to investigate the effects of replant soils on the growth of Malus domestica rootstock M26. Absolute quantification amplicon sequencing of 16S rRNA and ITS regions revealed a marked decline in rhizospheric microbial diversity in replant soils compared to fallow controls, accompanied by an enrichment of fungal genera such as Fusarium, Aspergillus, and Acremonium. Pathogenicity assays and seedling colonization experiments verified strong pathogenicity for five isolates—Acremonium sp., Aspergillus niger, Fusarium solani, Macrophomina phaseolina, and Aspergillus stellatus—implicating them as potential causal agents of ARD. High-throughput culturing and confrontation assays were used to isolate and screen candidate microbial antagonists. A synthetic microbiota (SynMs) composed of 12 bacterial strains and Trichoderma sp. was developed. Inoculation with SynMs significantly inproved plant height by 133% (P < 0.05) and total root length by 186% (P < 0.01), and effectively suppressed pathogen proliferation of the five pathogenic isolates in replant soils. Collectively, these findings identify key fungal pathogens underlying ARD and propose a sustainable microbiota-based strategy for its effective mitigation, offering both mechanistic insights and practical solutions for microbiome-informed orchard management.

Dwarfism is an important agronomic trait in fruit breeding programs. However, the germplasm resources required to generate dwarf pear (Pyrus spp.) varieties are limited. Moreover, the mechanisms underlying dwarfism remain unclear. In this study, “Yunnan” quince (Cydonia oblonga Mill.) had a dwarfing effect on “Zaosu” pear. Additionally, the dwarfism-related NAC transcription factor gene PbNAC71 was isolated from pear trees comprising “Zaosu” (scion) grafted onto “Yunnan” quince (rootstock). Transgenic Nicotiana benthamiana and pear OHF-333 (Pyrus communis) plants overexpressing PbNAC71 exhibited dwarfism, with a substantially smaller xylem and vessel area relative to the wild-type controls. Yeast one-hybrid, dual-luciferase, chromatin immunoprecipitation-qPCR, and electrophoretic mobility shift assays indicated that PbNAC71 downregulates PbWalls are thin 1 expression by binding to NAC-binding elements in its promoter. Yeast two-hybrid assays showed that PbNAC71 interacts with the E3 ubiquitin ligase PbRING finger protein 217 (PbRNF217). Furthermore, PbRNF217 promotes the ubiquitin-mediated degradation of PbNAC71 by the 26S proteasome, thereby regulating plant height as well as xylem and vessel development. Our findings reveal a mechanism underlying pear dwarfism and expand our understanding of the molecular basis of dwarfism in woody plants.

Dwarfing is an important agronomic characteristic in fruit breeding. However, due to the lack of dwarf cultivars and dwarf stocks, the dwarfing mechanism is poorly understood in pears. In this research, we discovered that the dwarf hybrid seedlings of pear (Pyrus bretschneideri Rehd.), ‘Red Zaosu,’ exhibited a xylem-deficient dwarf phenotype. The expression level of PbXND1, a suppressor of xylem development, was markedly enhanced in dwarf hybrid seedlings and its overexpression in pear results in a xylem-deficient dwarf phenotype. To further dissect the mechanism of PbXND1, PbTCP4 was isolated as a PbXND1 interaction protein through the pear yeast library. Root transformation experiments showed that PbTCP4 promotes root xylem development. Dual-luciferase assays showed that PbXND1 interactions with PbTCP4 suppressed the function of PbTCP4. PbXND1 expression resulted in a small amount of PbTCP4 sequestration in the cytoplasm and thereby prevented it from activating the gene expression, as assessed by bimolecular fluorescence complementation and co-location analyses. Additionally, PbXND1 affected the DNA-binding ability of PbTCP4, as determined by utilizing an electrophoretic mobility shift assay. These results suggest that PbXND1 regulates the function of PbTCP4 principally by affecting the DNA-binding ability of PbTCP4, whereas the cytoplasmic sequestration of PbTCP4 is only a minor factor. Taken together, this study provides new theoretical support for the extreme dwarfism associated with the absence of xylem caused by PbXND1, and it has significant reference value for the breeding of dwarf varieties and dwarf rootstocks of the pear.

‘Yunnan’ quince (Cydonia oblonga Mill.) is used as the dwarfing rootstock for pear (Pyrus spp.). Here, we reported that the sugar contents in mature ‘Zaosu’ pear fruit grafted on ‘Yunan’ quince (Z/Q) were higher than that in ‘Zaosu’ pear fruit grafted on ‘Duli’ (Pyrus betulifolia) (Z/D). To investigate the underlying mechanism, the leaf photosynthetic capacity and the leaf-to-fruit assimilate transport capacity were initially analyzed. The leaf photosynthetic capacity was similar between Z/Q and Z/D, but the assimilate transport capacity was greater for Z/Q than for Z/D. Sugar transporters mediate the distribution of assimilates; therefore, changes in PbSWEET transcriptional patterns were examined. PbSWEET6 was highly expressed in Z/Q fruit. Thus, the PbSWEET6 function related to assimilate transport was further verified. Sucrose and glucose contents increased in transgenic tomato fruit and pear fruit calli overexpressing PbSWEET6. Taken together, these results suggest that ‘Yunnan’ quince positively regulated fruit sugar contents by influencing the flow of PbSWEET6-involved assimilates in the scion.

Anthocyanins are common secondary metabolites in plants that impart red coloration to fruits and flowers. The important WRKY transcription factor family plays multifaceted roles in plant growth and development. In this study, we found a WRKY family gene, Pyrus bretschneideri WRKY75, that may be involved in anthocyanin synthesis in pear. Unlike Arabidopsis thaliana WRKY75, PbWRKY75 may be a positive regulator of anthocyanin synthesis. A transient expression assay indicated that PbWRKY75 promoted pear anthocyanin synthesis. The structural genes (PbANS, PbDFR, and PbUFGT) and positive regulators (PbMYB10 and PbMYB10b) of anthocyanin synthesis were significantly upregulated in the fruitlet skins of PbWRKY75‐overexpressing “Zaosu” pears. Subsequently, yeast one‐hybrid and dual‐luciferase assays indicated that PbWRKY75 promoted PbDFR, PbUFGT, and PbMYB10b expression by activating their promoters. These results revealed that PbWRKY75 may promote the expression of both PbMYB10b and anthocyanin late biosynthetic genes (PbDFR and PbUFGT) by activating their promoters, thereby inducing anthocyanin synthesis in pear. This study enhanced our understanding of the mechanism of pear anthocyanin synthesis, which will be beneficial in the improvement of pear peel color.

Differences in coloration exist among red pear cultivars. Here, we selected six red pear cultivars with different genetic backgrounds to elucidate the characteristics of fruit pigmentation. We detected anthocyanin contents and the expression levels of anthocyanin synthesis-related genes in these cultivars at different stages of fruit development. The anthocyanin contents of all six cultivars showed a rise–drop tendency. Principal component and hierarchical cluster analyses were used to distinguish the types of cultivars and the genes crucial to each anthocyanin accumulation pattern. The six cultivars were divided into three groups. Red Zaosu were clustered into one group, Red Sichou and Starkrimson into another group, and Palacer, Red Bartlett, and 5 Hao clustered into a third group. The expression levels of F3H, UFGT2, MYB10, and bHLH3 were similar among the differential coloration patterns of the six cultivars, suggesting a critical and coordinated mechanism for anthocyanin synthesis. Anthocyanin transporters (GST) and light-responsive genes, such as COP1, PIF3.1, and PIF3.2 played limited roles in the regulation of anthocyanin accumulation. This study provides novel insights into the regulation of anthocyanins synthesis and accumulation in red pears.