Studies on many plants have shown that mitogen-activated protein kinases (MAPKs) are key proteins involved in regulating plant responses to biotic and abiotic stresses. However, their involvement in cultivated strawberry development and ripening remains unclear. In this study, 43 FaMAPK gene family members were identified in the genome of cultivated strawberry (Fragaria × ananassa), phylogenetic analysis indicated that FaMAPKs could be classified into four groups. Systematic analysis of the conserved motif, exon–intron structure showed that there were significant varieties between different groups in structure, but in the same group they were similar. Multiple cis-regulatory elements associated with phytohormone response, and abiotic and biotic stresses were predicted in the promoter regions of FaMAPK genes. Transcriptional analysis showed that all FaMAPK genes were expressed at all developmental stages. Meanwhile, the effect of exogenous ABA and sucrose on the expression profile of FaMAPKs was investigated. Exogenous ABA, sucrose, and ABA plus sucrose treatments upregulated the expression of FaMAPK genes and increased the content of endogenous ABA, sucrose, and anthocyanin in strawberry fruits, suggesting that ABA and sucrose might be involved in the FaMAPK-mediated regulation of strawberry fruit ripening. Based on the obtained results, MAPK genes closely related to the ripening of strawberries were screened to provide a theoretical basis and support for future research on strawberries.

Fruit quality is strongly affected by genotype and harvest date. In this study, parameters regarding fruit quality, bioactive compounds, and antioxidant capacity of different strawberry cultivars at three harvesting dates were quantified to elucidate the influence of genotype and harvest date on strawberry quality. The results showed that harvest date was the major contributor to appearance color, TSS, TA, and TSS/TA ratio of strawberries, while genotype mainly affected firmness, anthocyanin content, and antioxidant capacity. Moreover, the interaction of genotype and harvest date had a primary influence on the content of ascorbic acid. The content of total phenolics and amino acids received the similar influence caused by genotype and harvest date. However, the interaction of genotype and harvest date significantly affected total phenolic content as well. These findings give a better understanding of the influence of the genotype and harvest date on strawberry, which might contribute to breed cultivars with more attractive fruits in terms of quality acceptance and nutritional value.

GR24, a synthetic strigolactone analogue, plays a crucial role in a wide range of life processes. Studying the effects of the pre-harvest application of GR24 on strawberry ripening and fruit quality provides a scientific basis for the application of GR24 in horticultural crop production. GR24 solutions at concentrations of 0, 0.5, 1 and 2 µmol/L were applied to strawberries at the de-greening stage. The results showed that pre-harvest treatment with 1 µmol/L GR24 increased fruit weight and size; promoted fruit softening; increased the content of sugars, total flavonoids, total phenolics, and anthocyanins, and increased antioxidant activity. These results proved that GR24 effectively accelerated fruit ripening and improved fruit quality. In addition, to gain more insight into the biological mechanism of GR24 in fruit ripening, we conducted a combined transcriptomic and metabolomic analysis. It was found that the differences were related to sugar and flavonoid biosynthesis, particularly in the later stage of fruit ripening. qRT-PCR analysis revealed that GR24 increased gene expression activity and metabolite accumulation in the anthocyanin and sugar biosynthetic pathway, thereby promoting strawberry color and flavor.

Ascorbic acid (AsA) is a crucial water-soluble antioxidant in strawberry fruit, but limited research is currently available on the identification and functional validation of key genes involved in AsA metabolism in strawberries. This study analyzed the FaMDHAR gene family identification, which includes 168 genes. Most of the products of these genes are predicted to exist in the chloroplast and cytoplasm. The promoter region is rich in cis-acting elements related to plant growth and development, stress and light response. Meanwhile, the key gene FaMDHAR50 that positively regulates AsA regeneration was identified through comparative transcriptome analysis of ‘Benihoppe’ strawberry (WT) and its natural mutant (MT) with high AsA content (83 mg/100 g FW). The transient overexpression experiment further showed that overexpression of FaMDHAR50 significantly enhanced the AsA content by 38% in strawberry fruit, with the upregulated expression of structural genes involved in AsA biosynthesis (FaGalUR and FaGalLDH) and recycling and degradation (FaAPX, FaAO and FaDHAR) compared with that of the control. Moreover, increased sugar (sucrose, glucose and fructose) contents and decreased firmness and citric acid contents were observed in the overexpressed fruit, which were accompanied by the upregulation of FaSNS, FaSPS, FaCEL1 and FaACL, as well as the downregulation of FaCS. Additionally, the content of pelargonidin 3-glucoside markedly decreased, while cyanidin chloride increased significantly. In summary, FaMDHAR50 is a key positive regulatory gene involved in AsA regeneration in strawberry fruit, which also plays an important role in the formation of fruit flavor, apperance and texture during strawberry fruit ripening.