Anthocyanins are a valuable source of antioxidants in the human diet and contribute to fruit coloration. In red-skinned pears, anthocyanin biosynthesis can be induced by light, in which the MYB–bHLH–WDR complex plays a critically important role in transcriptional regulation. However, knowledge of WRKY-mediated transcriptional regulation of light-induced anthocyanin biosynthesis is scarce in red pears. This work identified and functionally characterized a light-inducing WRKY transcription factor, PpWRKY44, in pear. Functional analysis based on overexpressed pear calli showed that PpWRKY44 promoted anthocyanin accumulation. Also, transiently overexpressed PpWRKY44 in pear leaves and fruit peels significantly enhanced the accumulation of anthocyanin, whereas silencing PpWRKY44 in pear fruit peels impaired induction of the accumulation of anthocyanin by light. By chromatin immunoprecipitation and electrophoretic mobility shift assay coupled to a quantitative polymerase chain reaction, we found that PpWRKY44 bound in vivo and in vitro to the PpMYB10 promoter, revealing it as a direct downstream target gene. Moreover, PpWRKY44 was activated by PpBBX18, a light signal transduction pathway component. Our results explained the mechanism mediating the impacts of PpWRKY44 on the transcriptional regulation of anthocyanin accumulation, with potential implications for fine-tuning the fruit peel coloration triggered by light in red pears.

Malate impacts fruit acidity and plays a vital role in stress tolerance. Malate accumulation is induced by salinity in various plants as a metabolite in coping with this stress. However, the exact molecular mechanism responsible for salinity-induced malate accumulation remains unclear. Here, we determined that salinity treatment induces malate accumulation in pear (Pyrus spp.) fruit, calli and plantlets compared to the control. Genetic and biochemical analyses established the key roles of PpWRKY44 and ABRE-BINDING FACTOR3 (PpABF3) transcription factors in promoting malate accumulation in response to salinity. We found that PpWRKY44 is involved in salinity-induced malate accumulation by directly binding to a W-box on the promoter of malate-associated gene aluminum-activated malate transporter 9 (PpALMT9) to activate its expression. A series of in-vivo and in-vitro assays revealed that the G-box cis-element in the promoter of PpWRKY44 was targeted by PpABF3, which further enhanced salinity-induced malate accumulation. Taken together, these findings suggest that PpWRKY44 and PpABF3 play positive roles in salinity-induced malate accumulation in pears. This research provides insights into the molecular mechanism by which salinity affects malate accumulation and fruit quality.

Bud dormancy is an important physiological process during winter. Its release requires a certain period of chilling. In pear (Pyrus pyrifolia), the abscisic acid (ABA)-induced expression of DORMANCY-ASSOCIATED MADS-box (DAM) genes represses bud break, whereas exogenous gibberellin (GA) promotes dormancy release. However, with the exception of ABA and GA, the regulatory effects of phytohormones on dormancy remain largely uncharacterized. In this study, we confirmed brassinosteroids (BRs) and jasmonic acid (JA) contribute to pear bud dormancy release. If chilling accumulation is insufficient, both 24-epibrassinolide (EBR) and methyl jasmonic acid (MeJA) can promote pear bud break, implying they positively regulate dormancy release. BRASSINAZOLE RESISTANT 2 (BZR2), which is a BR-responsive transcription factor, inhibited PpyDAM3 expression and accelerated pear bud break. The transient overexpression of PpyBZR2 increased endogenous GA, JA, and JA-Ile levels. In addition, the direct interaction between PpyBZR2 and MYELOCYTOMATOSIS 2 (PpyMYC2) enhanced the PpyMYC2-mediated activation of Gibberellin 20-oxidase genes PpyGA20OX1L1 and PpyGA20OX2L2 transcription, thereby increasing GA₃ contents and accelerating pear bud dormancy release. Interestingly, treatment with 5 µM MeJA increased the bud break rate, while also enhancing PpyMYC2-activated PpyGA20OX expression and increasing GA_3,4 contents. The 100 μM MeJA treatment decreased the PpyMYC2-mediated activation of the PpyGA20OX1L1 and PpyGA20OX2L2 promoters and suppressed the inhibitory effect of PpyBZR2 on PpyDAM3 transcription, ultimately inhibiting pear bud break. In summary, our data provide insights into the crosstalk between the BR and JA signaling pathways that regulate the BZR2/MYC2-mediated pathway in the pear dormancy release process.

Ethylene is an essential indicator of fruit ripening and climacteric or non-climacteric nature. This study investigated the postharvest behavior of five Chinese bayberry cultivars ‘Biqi’, ‘Dongkui’, ‘Fenhong’, ‘Xiazhihong’, and ‘Shuijing’. The fruits were harvested mature and stored at room temperature (25 °C) and under cold storage conditions (4 °C) to investigate the dynamics of ethylene production, firmness, anthocyanin content, and cell wall polysaccharide composition, as well as basic fruit physicochemical characteristics. The results show that Chinese bayberry is a climacteric fruit with ethylene production peaking shortly after harvest, especially at room temperature. Fruit color intensified over time due to anthocyanin accumulation, particularly in the flesh core. Darker cultivars produced more ethylene, which correlated with higher anthocyanin levels. At room temperature, ‘Biqi’ (black) had the highest ethylene production (4.03 µL·kg⁻¹·h⁻¹) and anthocyanin content (0.91 mg/g FW), while ‘Shuijing’, the white cultivar, had the lowest ethylene levels (1.9 µL·kg⁻¹·h⁻¹) and anthocyanin content (0.03 mg/g FW). Firmness significantly decreased at room temperature due to the degradation of hemicellulose and insoluble pectin, whereas cold storage mitigates this effect. After 3 days at room temperature, the average of firmness decreased by 23.7% in the five cultivars, compared to 12.7% under cold storage. Total soluble solids increase during storage, enhancing sweetness, especially at room temperature, with ‘Biqi’ increasing from 9.2 to 10.9% at 4 °C. Titratable acidity slightly decreased over time: the value for ‘Biqi’ decreased from 1.2% to 0.95% at room temperature and 1.1% at 4 °C. Citric, malic, and tartaric acid generally declined at room temperature but stabilized under cold storage. Sucrose, fructose, and glucose increased or remained stable, with significant varietal differences. Our results indicate that storing Chinese bayberry at 4 °C effectively preserves its quality and extends postharvest life. These findings underscore ethylene’s key role in regulating ripening, postharvest quality, and shelf life by influencing fruit color, firmness, and overall consumer appeal.

Color and acidity, two important fruit quality traits, greatly influence consumer choice and market competitiveness. They result from the accumulation of anthocyanins and organic acids in the vacuole. A shift in the vacuolar pH, caused by the accumulation of organic acids, leads to a change in the absorption spectrum of anthocyanins, and thus to changes in the color of tissues, suggesting a possible relationship between these two traits. Thus, the discovery of the molecular co-mechanism responsible for these processes is one of the most challenging for improving fruit quality traits and ultimately increasing market value. Here, we review current knowledge on the relationship between anthocyanin accumulation and acidity, and highlight recent advances in the roles of TFs in regulating these quality traits via transcriptional co-regulation of different genes associated with anthocyanin accumulation and acidity for fruit quality improvement.