Downregulation of RdDM during strawberry fruit ripening

Background

Recently, DNA methylation was proposed to regulate fleshy fruit ripening. Fleshy fruits can be distinguished by their ripening process as climacteric fruits, such as tomatoes, or non-climacteric fruits, such as strawberries. Tomatoes undergo a global decrease in DNA methylation during ripening, due to increased expression of a DNA demethylase gene. The dynamics and biological relevance of DNA methylation during the ripening of non-climacteric fruits are unknown.

Results

Here, we generate single-base resolution maps of the DNA methylome in immature and ripe strawberry. We observe an overall loss of DNA methylation during strawberry fruit ripening. Thus, ripening-induced DNA hypomethylation occurs not only in climacteric fruit, but also in non-climacteric fruit. Application of a DNA methylation inhibitor causes an early ripening phenotype, suggesting that DNA hypomethylation is important for strawberry fruit ripening. The mechanisms underlying DNA hypomethylation during the ripening of tomato and strawberry are distinct. Unlike in tomatoes, DNA demethylase genes are not upregulated during the ripening of strawberries. Instead, genes involved in RNA-directed DNA methylation are downregulated during strawberry ripening. Further, ripening-induced DNA hypomethylation is associated with decreased siRNA levels, consistent with reduced RdDM activity. Therefore, we propose that a downregulation of RdDM contributes to DNA hypomethylation during strawberry ripening.

Conclusions

Our findings provide new insight into the DNA methylation dynamics during the ripening of non-climacteric fruit and suggest a novel function of RdDM in regulating an important process in plant development.

     

Interaction between QTLs induces an advance in ethylene biosynthesis during melon fruit ripening

The coexistence of both climacteric and non-climacteric genotypes and the availability of a set of genetic and genomic resources make melon a suitable model for genetic studies of fruit ripening. We have previously described a QTL, ETHQB3.5, which induces climacteric fruit ripening in the near-isogenic line (NIL) SC3-5 that harbors an introgression on linkage group (LG) III from the non-climacteric melon accession PI 161375 in the, also non-climacteric cultivar, “Piel de Sapo” genetic background. In the current study, a new major QTL, ETHQV6.3, on LG VI was detected on an additional introgression in the same NIL. These QTLs are capable, individually, of inducing climacteric ripening in the non-climacteric background, the effects of ETHQV6.3 being greater than that of ETHQB3.5. The QTLs interact epistatically, advancing the timing of ethylene biosynthesis during ripening and, therefore, the climacteric responses. ETHQV6.3 was fine-mapped to a 4.5 Mb physical region of the melon genome, probably in the centromeric region of LG VI. The results presented will be of value in the molecular identification of the gene underlying ETHQV6.3     

Isolation and characterization of mRNAs differentially expressed during ripening of wild strawberry (Fragaria vesca L.) fruits

Wild strawberry (Fragaria vesca L.) is an attactive model system for studying ripening in non-climacteric fruit, because of its small diploid genome, its short reproductive cycle, and its capacity for transformation. We have isolated eight ripening-induced cDNAs from this species after differential screening of a cDNA library. The predicted polypeptides of seven of the clones exhibit similarity to database protein sequences, including acyl carrier protein, caffeoyl- CoA 3-O-methyltransferase, sesquiterpene cyclase, major latex protein, cystathionine -synthase, dehydrin and an auxin- induced gene. A ninth cDNA clone that was constitutively expressed is predicted to encode a metallothionein-like protein. None of these proteins appear to be directly related to events generally associated with ripening such as cell wall metabolism or the accumulation of sugars and pigments, rather, their putative functions are indicative of the wide range of processes upregulated during fruit ripening.     

Candidate genes and QTLs for fruit ripening and softening in melon

Different factors affect the quality of melon fruit and among them long shelf life is critical from the consumer’s point of view. In melon, cultivars showing both climacteric and non-climacteric ripening types are found. In this study we have investigated climacteric ripening and fruit softening using a collection of near-isogenic lines (NILs) derived from the non-climacteric melon parental lines PI 161375 (SC) and “Piel de Sapo” (PS). Surprisingly, we found that QTL eth3.5 in NIL SC3-5b induced a climacteric-ripening phenotype with increased respiration and ethylene levels. Data suggest that the non-climacteric phenotypes from PI 161375 and “Piel de Sapo” may be the result of mutations in different genes. Several QTLs for fruit flesh firmness were also detected. Candidate genes putatively involved in ethylene regulation, biosynthesis and perception and cell wall degradation were mapped and some colocations with QTLs were observed. These results may provide additional data towards understanding of non-climacteric ripening in melon.     

Interactions Between Strawberry ABA Receptor PYR/PYLs and Protein Phosphatase PP2Cs on Basis of Transcriptome and Yeast Two-Hybrid Analyses

Journal of Plant Growth Regulation - Strawberry (Fragaria × ananassa) is an ideal model plant for studies on non-climacteric fruit ripening. Although much progress has been...     

Transformation of a marker-free and vector-free antisense ACC oxidase gene cassette into melon via the pollen-tube pathway

Purpose of work  

Melons have short shelf-lives due to fruit ripening caused by ethylene production. The 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase gene is essential for ethylene biosynthesis. As fruit ripening in other fruit crops can be deterred by down-regulation of ACC oxidase expression, we have carried out similar work to improve fruit quality and shelf-life of the melon Cucumis melo.     

Characterization of a calcium/calmodulin-regulated SR/CAMTA gene family during tomato fruit development and ripening

Background  

Fruit ripening is a complicated development process affected by a variety of external and internal cues. It is well established that calcium treatment delays fruit ripening and senescence. However, the underlying molecular mechanisms remain unclear.     

Reciprocity between abscisic acid and ethylene at the onset of berry ripening and after harvest

Background  

The ripening of grape berry is generally regulated by abscisic acid (ABA), and has no relationship with ethylene function. However, functional interaction and synergism between ABA and ethylene during the beginning of grape berry ripening (véraison) has been found recently.     

An expansin gene expressed in ripening strawberry fruit

Tissue softening accompanies the ripening of many fruit and initiates the processes of irreversible deterioration. Expansins are plant cell wall proteins proposed to disrupt hydrogen bonds within the cell wall polymer matrix. Expression of specific expansin genes has been observed in tomato (Lycopersicon esculentum) meristems, expanding tissues, and ripening fruit. It has been proposed that a tomato ripening-regulated expansin might contribute to cell wall polymer disassembly and fruit softening by increasing the accessibility of specific cell wall polymers to hydrolase action. To assess whether ripening-regulated expansins are present in all ripening fruit, we examined expansin gene expression in strawberry (Fragaria x ananassa Duch.). Strawberry differs significantly from tomato in that the fruit is derived from receptacle rather than ovary tissue and strawberry is non-climacteric. A full-length cDNA encoding a ripening-regulated expansin, FaExp2, was isolated from strawberry fruit. The deduced amino acid sequence of FaExp2 is most closely related to an expansin expressed in early tomato development and to expansins expressed in apricot fruit rather than the previously identified tomato ripening-regulated expansin, LeExp1. Nearly all previously identified ripening-regulated genes in strawberry are negatively regulated by auxin. Surprisingly, FaExp2 expression was largely unaffected by auxin. Overall, our results suggest that expansins are a common component of ripening and that non-climacteric signals other than auxin may coordinate the onset of ripening in strawberry.     

ClSnRK2.3 negatively regulates watermelon fruit ripening and sugar accumulation

Watermelon(Citrullus lanatus) as non-climacteric fruit is domesticated from the ancestors with inedible fruits. We previously revealed that the abscisic acid(ABA) signaling pathway gene ClSnRK2.3 might infuence watermelon fruit ripening. However,the molecular mechanisms are unclear. Here,we found that the selective variation of ClSnRK2.3 resulted in lower promoter activity and gene expression level in cultivated watermelons than ancestors, which indicated ClSnRK2.3 might be a negative regulator ...     

Ozone-induced inhibition of kiwifruit ripening is amplified by 1-methylcyclopropene and reversed by exogenous ethylene

Background

Understanding the mechanisms involved in climacteric fruit ripening is key to improve fruit harvest quality and postharvest performance. Kiwifruit (Actinidia deliciosa cv. ‘Hayward’) ripening involves a series of metabolic changes regulated by ethylene. Although 1-methylcyclopropene (1-MCP, inhibitor of ethylene action) or ozone (O₃) exposure suppresses ethylene-related kiwifruit ripening, how these molecules interact during ripening is unknown.

Results

Harvested ‘Hayward’ kiwifruits were treated with 1-MCP and exposed to ethylene-free cold storage (0?°C, RH 95%) with ambient atmosphere (control) or atmosphere enriched with O₃ (0.3?μL?L^??1) for up to 6?months. Their subsequent ripening performance at 20?°C (90% RH) was characterized. Treatment with either 1-MCP or O₃ inhibited endogenous ethylene biosynthesis and delayed fruit ripening at 20?°C. 1-MCP and O₃ in combination severely inhibited kiwifruit ripening, significantly extending fruit storage potential. To characterize ethylene sensitivity of kiwifruit following 1-MCP and O₃ treatments, fruit were exposed to exogenous ethylene (100?μL?L^??1, 24?h) upon transfer to 20?°C following 4 and 6?months of cold storage. Exogenous ethylene treatment restored ethylene biosynthesis in fruit previously exposed in an O₃-enriched atmosphere. Comparative proteomics analysis showed separate kiwifruit ripening responses, unraveled common 1-MCP- and O₃-dependent metabolic pathways and identified specific proteins associated with these different ripening behaviors. Protein components that were differentially expressed following exogenous ethylene exposure after 1-MCP or O₃ treatment were identified and their protein-protein interaction networks were determined. The expression of several kiwifruit ripening related genes, such as 1-aminocyclopropane-1-carboxylic acid oxidase (ACO1), ethylene receptor (ETR1), lipoxygenase (LOX1), geranylgeranyl diphosphate synthase (GGP1), and expansin (EXP2), was strongly affected by O₃, 1-MCP, their combination, and exogenously applied ethylene.

Conclusions

Our findings suggest that the combination of 1-MCP and O₃ functions as a robust repressive modulator of kiwifruit ripening and provide new insight into the metabolic events underlying ethylene-induced and ethylene-independent ripening outcomes.

     

Ethylene and fruit ripening

The latest advances in our understanding of the relationship between ethylene and fruit ripening are reviewed. Considerable progress has been made in the characterisation of genes encoding the key ethylene biosynthetic enzymes, ACC synthase (ACS) and ACC oxidase (ACO) and in the isolation of genes involved in the ethylene signal transduction pathway, particularly those encoding ethylene receptors ( ETR ). These have allowed the generation of transgenic fruit with reduced ethylene production and the identification of the Nr tomato ripening mutant as an ethylene receptor mutant. Through these tools, a clearer picture of the role of ethylene in fruit ripening is now emerging. In climacteric fruit, the transition to autocatalytic ethylene production appears to result from a series of events where developmentally regulated ACO and ACS gene expression initiates a rise in ethylene production, setting in motion the activation of autocatalytic ethylene production. Differential expression of ACS and ACO gene family members is probably involved in such a transition. Finally, we discuss evidence suggesting that the NR ethylene perception and transduction pathway is specific to a defined set of genes expressed in ripening climacteric fruit and that a distinct ETR pathway regulates other ethylene-regulated genes in both immature and ripening climacteric fruit as well as in non-climacteric fruit. The emerging picture is one where both ethylene-dependent and -independent pathways coexist in both climacteric and non-climacteric fruits. Further work is needed in order to dissect the molecular events involved in individual ripening processes and to understand the regulation of the expression of both ethylene-dependent and -independent genes.