Combined transcriptomic and proteomic analysis reveals multiple pathways involved in self-pollen tube development and the potential roles of FviYABBY1 in self-incompatibility in Fragaria viridis.

Fragaria viridis exhibits S-RNase-based gametophytic self-incompatibility, in which S-RNase is the major factor inhibiting pollen tube growth. However, the pathways involved in and the immediate causes of the inhibition of pollen tube growth remain unknown. Here, interactive RNA sequencing and proteome analysis revealed changes in the transcriptomic and proteomic profiles of F. viridis styles harvested at 0 and 24 h after self-pollination. A total of 2,181 differentially expressed genes and 200 differentially abundant proteins were identified during the pollen development stage of self-pollination. Differentially expressed genes and differentially abundant proteins associated with self-incompatible pollination were further mined, and multiple pathways were found to be involved. Interestingly, the expression pattern of the transcription factor FviYABBY1, which is linked to polar growth, differed from those of other genes within the same family. Specifically, FviYABBY1 expression was extremely high in pollen, and its expression trend in self-pollinated styles was consistent with that of S-RNase. Furthermore, FviYABBY1 interacted with S-RNase in a non-S haplotype way. Therefore, FviYABBY1 affects the expression of polar growth-related genes in self-pollen tubes and is positively regulated by S-RNase.

Melatonin Alleviates Drought Stress by a Non-Enzymatic and Enzymatic Antioxidative System in Kiwifruit Seedlings.

Although melatonin was affirmed to alleviate drought stress in various plant species, the mechanism in kiwifruit remains to be elucidated. In this study, the transcriptomes of kiwifruit leaves under control (CK), DR (drought stress), and MTDR (drought plus melatonin) treatments were evaluated. After comparisons of the gene expression between DR and MTDR, the differentially expressed genes (DEGs) were screened. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses indicated three significant pathways, which were mainly involved in the glutathione metabolism, ascorbate and aldarate metabolism, and carotenoid metabolism. Therefore, the content and metabolic gene expression level of ascorbic acid (AsA), glutathione, and carotenoid were higher in the MTDR treatment than that in others. Furthermore, the activity and mRNA expression level of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) were also promoted in the MTDR group. Combined with these results of important secondary metabolites and protective enzymes measured in the seedlings in different treatments, it could be concluded that exogenous melatonin induced the ascorbic acid-glutathione (AsA-GSH) cycle, carotenoid biosynthesis, and protective enzyme system to improve seedling growth. Our results contribute to the development of a practical method for kiwifruit against drought stress.

Exogenous Melatonin Application Delays Senescence of Kiwifruit Leaves by Regulating the Antioxidant Capacity and Biosynthesis of Flavonoids.

Melatonin, a multiple signal molecule, plays important roles in delaying senescence during the development of plants. Because few species have been studied for the effect of exogenous melatonin on anti-aging, the plausible mechanism of melatonin of anti-aging effects on other plant species has remained largely unknown. In the present study, the effects of exogenous melatonin on leaf senescence in kiwifruit were examined during natural aging after melatonin (200 µM) or water (Control) pretreatment. The decreased membrane damage and lower hydrogen peroxide (H2O2) content due to the enhanced scavenging activity of antioxidant enzymes peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT) demonstrated that melatonin effectively delayed the aging of kiwifruit leaves. Likewise, owing to up-regulated expression of chlorophyll a/b-binding protein (CAB) gene in the sampled leaves pretreated with melatonin, chlorophyll degradation decreased. Therefore, osmoregulatory substances in sampled leaves accumulated (e.g., soluble sugar and soluble protein) and seedling cell environment stability was maintained. Simultaneously, melatonin decreased H2O2 concentration owing to increased glutathione (GSH) and ascorbate (AsA) content, and the expression levels of glutathione reductase (GR), ascorbate peroxidase (APX), monodehydroascorbate reductase (MDAR), dehydroascorbate reductase (DHAR) were up-regulated by melatonin application, indicating that the increase of GSH and AsA was attributed to the expression of these genes. In addition, a large amount of flavonoids accumulated in seedlings pretreated with melatonin, and transcript levels of eight genes involved in flavonoid synthesis, including phenylalanine ammonia-lyase (PAL), cinnamate-4-hydroxymate (C4H), chalcone synthase (CHS), flavanone 3-hydroxylase (F3H), flavonol synthase (FNS), leucoanthocyanin reductase (LAR), anthocyanin reductase (ANR), flavonoid 3-O-glucosyltransferase (UFGT) were enhanced in response to melatonin application. These results indicated that melatonin delayed aging of kiwifruit leaves by activating the antioxidant capacity and enhancing flavonoid biosynthesis. All of these results can provide clear proof that melatonin plays a key roles in delaying leaf senescence.

Melatonin Improves Heat Tolerance in Kiwifruit Seedlings through Promoting Antioxidant Enzymatic Activity and Glutathione S-Transferase Transcription.

Evidence exists to suggest that melatonin (MT) is important to abiotic stress tolerance in plants. Here, we investigated whether exogenous MT reduces heat damage on biological parameters and gene expression in kiwifruit (Actinidia deliciosa) seedlings. Pretreatment with MT alleviates heat-induced oxidative harm through reducing H2O2 content and increasing proline content. Moreover, MT application raised ascorbic acid (AsA) levels and the activity of antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD). We also observed elevation in the activity of enzymes related to the AsA-GSH cycle, such as ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), and glutathione reductase (GR). Furthermore, MT application increased the expression of 28/31 glutathione S-transferase (GST) genes, reducing oxidative stress. These results clearly indicate that in kiwifruit, MT exerts a protective effect against heat-related damage through regulating antioxidant pathways.

Ascorbic acid metabolism during sweet cherry (Prunus avium) fruit development.

To elucidate metabolism of ascorbic acid (AsA) in sweet cherry fruit (Prunus avium 'Hongdeng'), we quantified AsA concentration, cloned sequences involved in AsA metabolism and investigated their mRNA expression levels, and determined the activity levels of selected enzymes during fruit development and maturation. We found that AsA concentration was highest at the petal-fall period (0 days after anthesis) and decreased progressively during ripening, but with a slight increase at maturity. AsA did nevertheless continue to accumulate over time because of the increase in fruit fresh weight. Full-length cDNAs of 10 genes involved in the L-galactose pathway of AsA biosynthesis and 10 involved in recycling were obtained. Gene expression patterns of GDP-L-galactose phosphorylase (GGP2), L-galactono-1, 4-lactone dehydrogenase (GalLDH), ascorbate peroxidase (APX3), ascorbate oxidase (AO2), glutathione reductase (GR1), and dehydroascorbate reductase (DHAR1) were in accordance with the AsA concentration pattern during fruit development, indicating that genes involved in ascorbic acid biosynthesis, degradation, and recycling worked in concert to regulate ascorbic acid accumulation in sweet cherry fruit.