Ethylene biosynthesis and signal transduction during ripening and softening in non-climacteric fruits: an overview.

In recent years, the ethylene-mediated ripening and softening of non-climacteric fruits have been widely mentioned. In this paper, recent research into the ethylene-mediated ripening and softening of non-climacteric fruits is summarized, including the involvement of ethylene biosynthesis and signal transduction. In addition, detailed studies on how ethylene interacts with other hormones to regulate the ripening and softening of non-climacteric fruits are also reviewed. These findings reveal that many regulators of ethylene biosynthesis and signal transduction are linked with the ripening and softening of non-climacteric fruits. Meanwhile, the perspectives of future research on the regulation of ethylene in non-climacteric fruit are also proposed. The overview of the progress of ethylene on the ripening and softening of non-climacteric fruit will aid in the identification and characterization of key genes associated with ethylene perception and signal transduction during non-climacteric fruit ripening and softening.

Light influences the effect of exogenous ethylene on the phenolic composition of Cabernet Sauvignon grapes.

The gaseous phytohormone ethylene (ETH) plays a key role in plant growth and development, and is a major regulator of phenolic biosynthesis. Light has long been known to influence phytohormone signaling transduction. However, whether light influences the effect of ETH on the phenolic composition of grapes (Vitis vinifera L.) is an open question. Here, the accumulation and composition of anthocyanins and non-anthocyanin phenolics were analyzed in Cabernet Sauvignon grapes under four treatments: light exposure with and without ETH treatment, and box-shading with and without ETH treatment. Both light and ETH promoted ripening, decreased the color index (L*, C*, and h*), and accelerated the color change from green to red and purplish red. Sunlight-exposed grapes had the highest contents of most anthocyanins, flavonols, flavan-3-ols, and hydroxybenzoic acids. In addition, light exposure increased the ratios of 3'5'-substituted/3'-substituted anthocyanins and flavonols, but decreased the ratios of methoxylated/non-methoxylated and acylated/non-acylated anthocyanins and flavan-3-ols. Notably, the effects of ETH were influenced by light exposure. Specifically, ETH treatment promoted anthocyanin and non-anthocyanin biosynthesis in light-exposed grapes, and their increasing multiples were remarkably higher under light-exposed conditions. Furthermore, ETH treatment decreased the ratios of methoxylated/non-methoxylated, 3'5'-substituted/3'-substituted, and acylated/non-acylated anthocyanins and flavan-3-ols in light-exposed grapes, each of which was increased by ETH treatment in shaded grapes. Fifteen differential phenolic components were identified through partial least-squares-discriminant analysis (PLS-DA). Among them, cyanidin-3-O-(cis-6-O-coumaryl)-glucoside, petunidin-3-O-(6-O-acetyl)-glucoside, petunidin-3-O-(trans-6-O-coumaryl)-glucoside, petunidin-3-O-glucoside, myricetin-3-O-galactoside, kaempferol-3-O-galactoside, and kaempferol-3-O-glucoside were the main differential components between ETH treatments under different light conditions. This study contributes to the understanding of the impact of ethylene treatment under dark and light conditions on phenolic synthesis in grape berries.

Transcription factors DkBZR1/2 regulate cell wall degradation genes and ethylene biosynthesis genes during persimmon fruit ripening.

BRASSINAZOLE RESISTANT (BZR) transcription factors are critical components of the brassinosteroid signalling pathway, but their possible roles in fruit ripening have rarely been reported. In this study, four BZR sequences were isolated from persimmon fruit. Among the four BZR genes, DkBZR1/2 were expressed in persimmon fruit; DkBZR1 protein amount decreased and dephosphorylated DkBZR2 gradually accumulated during the storage period. DkBZR1/2 proteins were localized in both the nucleus and cytoplasm and accumulated in the nucleus after 24-epibrassinolide treatment. DkBZR1 suppressed the transcription of Diospyros kaki endo-1,4-betaglucanase 1 (DkEGase1) and 1-aminocyclopropane-1-carboxylate synthase 1 (DkACS1) by binding to the BR response element (BRRE) in their promoters, and DkBZR2 activated the transcription of pectate lyase 1 (DkPL1) and 1-aminocyclopropane-1-carboxylate oxidase 2 (DkACO2) by binding to the E-box motif in their promoters. Transient overexpression of DkBZR2 promoted the conversion of acid-soluble pectin to water-soluble pectin and increased ethylene production in persimmon fruit. Our findings indicate that DkBZR1 and DkBZR2 serve as repressors and activators of persimmon fruit ripening, respectively.

High-CO2/Hypoxia-Responsive Transcription Factors DkERF24 and DkWRKY1 Interact and Activate DkPDC2 Promoter.

Identification and functional characterization of hypoxia-responsive transcription factors is important for understanding plant responses to natural anaerobic environments and during storage and transport of fresh horticultural products. In this study, yeast one-hybrid library screening using the persimmon (Diospyros kaki) pyruvate decarboxylase (DkPDC2) promoter identified three ethylene response factor (ERF) genes (DkERF23/DkERF24/DkERF25) and four WRKY transcription factor genes (DkWRKY/DdkWRKY5/DkWRKY6/DkWRKY7) that were differentially expressed in response to high CO2 (95%, with 4% N2 and 1% oxygen) and high N2 (99% N2 and 1% oxygen). Yeast one-hybrid assays and electrophoretic mobility shift assays indicated that DkERF23, DkERF24, DkERF25, DkWRKY6, and DkWRKY7 could directly bind to the DkPDC2 promoter. Dual-luciferase assays confirmed that these transcription factors were capable of transactivating the DkPDC2 promoter. DkERF24 and DkWRKY1 in combination synergistically transactivated the DkPDC2 promoter, and yeast two-hybrid and bimolecular fluorescence complementation assays confirmed protein-protein interaction between DkERF24 and DkWRKY1. Transient overexpression of DkERF24 and DkWRKY1 separately and in combination in persimmon fruit discs was effective in maintaining insolubilization of tannins, concomitantly with the accumulation of DkPDC2 transcripts. Studies with Arabidopsis (Arabidopsis thaliana) homologs AtERF1 and AtWRKY53 indicated that similar protein-protein interactions and synergistic regulatory effects also occur with the DkPDC2 promoter. We propose that an ERF and WRKY transcription factor complex contributes to responses to hypoxia in both persimmon fruit and Arabidopsis, and the possibility that this is a general plant response requires further investigation.

Identification of xyloglucan endotransglucosylase/hydrolase genes (XTHs) and their expression in persimmon fruit as influenced by 1-methylcyclopropene and gibberellic acid during storage at ambient temperature.

Xyloglucan endotransglucosylase/hydrolase (XTH) is thought to contribute to fruit softening by degrading xyloglucan that is a predominant hemicellulose in the cell wall. In this study, two full-length XTH genes (DKXTH1 and DKXTH2) were identified from 'Fupingjianshi' persimmon fruit, and the expression level of both XTH genes was investigated during softening for 18-24 d using RT-qPCR. Sequence analysis showed that DKXTH1 and DKXTH2 contained a putative open reading frame of 861 and 876 bp encoding polypeptides of 287 and 292 amino acid residues, respectively, which contained the conserved DEIDFEFLG motif of XTH, a potential N-linked glycosylation signal site. RT-qPCR analysis showed that DKXTH1 and DKXTH2 in untreated fruit had different expression patterns during fruit softening, in which maximum expression occurred on days 3 and 12 of ripening, respectively. 1-Methylcyclopropene (1-MCP) and gibberellic acid (GA(3)) treatments delayed the softening and ethylene peak of persimmon fruit, as well as suppressed the expression of both XTH genes, especially DKXTH1. These results indicated that the expression of both XTH genes might be ethylene dependent action, and closely related to softening of persimmon in the early (DKXTH1) and later (DKXTH2) ripening stages.