Tissue-specific transcriptional analysis outlines calcium-induced core metabolic changes in sweet cherry fruit

Integrated analysis of transcriptome and microRNAs associated with exogenous calcium-mediated enhancement of hypoxic tolerance in cucumber seedlings (Cucumis sativus L.)

Plants often suffer from hypoxic stress due to flooding caused by extreme weather. Hypoxia usually leads to restricted oxygen supply and alters metabolic patterns from aerobic to anaerobic. Cucumber roots are fragile and highly sensitive to damage from hypoxic stress. The purpose of this study was to investigate the regulatory mechanism of exogenous calcium alleviating hypoxic stress in cucumber through transcriptome and small RNAs analysis. Three treatments were performed in this paper, including untreated-control (CK), hypoxic stress (H), and hypoxic stress + exogenous calcium treatment (H + Ca²⁺). A large number of differentially expressed genes (DEGs) were identified, 1,463 DEGs between CK vs H, 3,399 DEGs between H vs H + Ca²⁺, and 5,072 DEGs between CK vs H + Ca²⁺, respectively. KEGG analysis of DEGs showed that exogenous calcium could activate hormone signaling pathways (ethylene, ABA, IAA and cytokinin), transcription factors (MYB, MYB-related, bHLH, bZIP, and WRKY), calcium signaling and glycolysis pathway to mitigating hypoxic stress in cucumber seedlings. Additionally, miRNA and their target genes were detected and predicted between treatments. The target genes of these miRNAs revealed that auxin, cellulose synthase, and mitochondrial ribosomal related genes (Csa2G315390, Csa6G141390, Csa4G053280, and Csa6G310480) probably play in the improvement of the hypoxic tolerance of cucumber seedlings through exogenous calcium application. In short, our data adds new information to the mechanism of exogenous calcium mitigation of hypoxic stress injury in cucumber seedlings at transcriptional and post-transcriptional levels.

Effects of calcium on cell wall metabolism enzymes and expression of related genes associated with peel creasing in Citrus fruits

Fruit peel creasing is a serious pre-harvest physiological disorder in citrus, influencing fruit quality, storage, and yield. Four- and eight-year-old 'Hongjiang' oranges grafted onto Canton lemon rootstocks were treated with calcium and calcium inhibitors, respectively, to study the effects of different treatments on fruit creasing rate, mechanical properties of the peel, cell wall metabolism enzyme activities, and the expression of related genes. Foliar application of 0.5% calcium nitrate significantly reduced the fruit creasing rate, while treatment with EGTA and LaCl₃, inhibitors of calcium uptake, increased the fruit creasing rate; But the effect of calcium nitrate treatment on changing the mechanical properties of pericarp and inhibiting the activity of hydrolase (PG, Cx and PE) was not very significant. Furthermore, it was observed that the expression levels of genes (PG, Cx, and PE) encoding cell wall-degrading enzymes were significantly lower in the normal fruit peel than in the creased fruit peel. Meanwhile, the expression levels of PG, Cx, and PE were higher in the peel of shaded fruit than in the peel of exposed fruit. During the high incidence period of fruit creasing, calcium nitrate treatment down-regulated the expression of PG, Cx, and PE, while EGTA treatment up-regulated the expression of these genes. In conclusion, foliar spraying of calcium nitrate at the fruit rapid enlargement stage can increase the Ca content in the peel of 'Hongjiang' orange and significantly suppress the expression of cell wall degrading enzymes genes (PG, PE and Cx) in 'Hongjiang' orange peel during the high occurrence period of fruit creasing, resulting in reducing the occurrence of fruit creasing and cracking.