Search

Although the role of the ethylene response factor (ERF) Pti4 in disease resistance has been demonstrated in higher plants, it is presently unknown whether the tomato SlPti4 protein plays a role in the regulation of fruit development and the stress response. Here, we show that SlPti4 is involved in the regulation of fruit ripening, seed germination, and responses to drought and Botrytis cinerea infection through adjustments to ABA metabolism and signaling. SlPti4 gene expression is very low early in fruit development, but increases rapidly during ripening and can be induced by exogenous ABA and 1-aminocyclopropane 1-carboxylate (ACC). RNA interference (RNAi)-induced silencing of SlPti4 leads to an increase of ABA accumulation together with a decrease of ethylene release, which causes the high expression level of SlBcyc, and thus the transgenic fruit is orange instead of red as in wild-type fruit during ripening. SlPti4 -RNAi seeds accumulate less ABA and mRNA for ABA receptor SlPYL genes, which causes insensitivity to ABA treatment. SlPti4 -RNAi transgenic plants with low ABA levels and high ethylene release were more sensitive to drought stress. SlPti4 -RNAi plants also showed weaker resistance to B. cinerea infection than the wild type. Thus, SlPti4 is an important regulator of tomato fruit ripening, seed germination and abiotic/biotic stress responses. This study expands our knowledge on diverse plant physiologies which are regulated by ABA signaling and the function of SlPti4. [ABSTRACT FROM AUTHOR]

Abscisic acid ( ABA) glucose conjugation mediated by uridine diphosphate glucosyltransferases ( UGTs) is an important pathway in regulating ABA homeostasis. In the present study, we investigated three tomato Sl UGTs that are highly expressed in fruit during ripening, and these Sl UGTs were localized to the cytoplasm and cell nucleus. Among these three UGTs, Sl UGT75C1 catalyzes the glucosylation of both ABA and IAA in vitro; Sl UGT76E1 can only catalyze the conjugation of ABA; and Sl UGT73C4 cannot glycosylate either ABA or IAA. Therefore, Sl UGT75C1 was selected for further investigation. Sl UGT75C1 RNA interference significantly up-regulated the expression level of Sl CYP707A2, which encodes an ABA 8′-hydroxylase but did not affect the expression of Sl NCED1, which encodes a key enzyme in ABA biosynthesis. Suppression of Sl UGT75C1 significantly accelerated fruit ripening by enhancing ABA levels and promoting the early release of ethylene. Sl UGT75C1- RNAi altered the expression of fruit ripening genes (genes involved in ethylene release and cell wall catabolism). Sl UGT75C1- RNAi seeds showed delayed germination and root growth compared with wild-type as well as increased sensitivity to exogenous ABA. Sl UGT75C1- RNAi plants were also more resistant to drought stress. These results demonstrated that Sl UGT75C1 plays a crucial role in ABA-mediated fruit ripening, seed germination, and drought responses in tomato. [ABSTRACT FROM AUTHOR]

In plants, β-glucosidases ( BG) have been implicated in developmental and pathogen defense, and are thought to take part in abscisic acid ( ABA) synthesis via hydrolysis of ABA glucose ester to release active ABA; however, there is no genetic evidence for the role of BG genes in ripening and biotic/abiotic stress in fruits. To clarify the role of BG genes in fruit, eight Fa/Fv BG genes encoding β-glucosidase were isolated using information from the GenBank strawberry nucleotide database. Of the Fa/Fv BG genes examined, expression of Fa BG3 was the highest, showing peaks at the mature stage, coincident with the changes observed in ABA content. To verify the role of this gene, we suppressed the expression of Fa BG3 via inoculation with Agrobacterium tumefaciens containing tobacco rattle virus carrying a Fa BG3 fragment ( RNAi). The expression of Fa BG3 in Fa BG3- RNAi-treated fruit was markedly reduced, and the ABA content was lower than that of the control. Fa BG3- RNAi-treated fruit did not exhibit full ripening, and were firmer, had lower sugar content, and were pale compared with the control due to down-regulation of ripening-related genes. Fa BG3- RNAi-treated fruit with reduced ABA levels were much more resistant to Botrytis cinerea fungus but were more sensitive to dehydration stress than control fruit. These results indicate that Fa BG3 may play key roles in fruit ripening, dehydration stress and B. cinerea fungal infection in strawberries via modulation of ABA homeostasis and transcriptional regulation of ripening-related genes. [ABSTRACT FROM AUTHOR]

The VlMYBA subfamily of transcription factors has been known to be the functional regulators in anthocyanin biosynthesis in red grapes. In this study, the expressions of the VlMYBA1-2 and VlMYBA 2 genes, and the responses of the VlMYBA1-2/2 promoters to ABA and ACC treatments in Kyoho grape berries are examined through quantitative real-time PCR analysis and the transient expression assay. The results show that the expressions of VlMYBA1-2/2 increase dramatically after véraison and reach their highest levels when the berries are nearly fully ripe. Exogenous ABA promotes the expressions of VlMYBA1-2/2 , whereas the ACC treatment increases the expression of VlMYBA2 , however, it has no effect on VlMYBA1-2 . The ABA treatment has a faster and stronger effect on berry pigmentation than ACC does. The VlMYBA1-2 promoter sequence contains two ABA response elements (ABRE) but no ethylene response element (ERE), whereas the VlMYBA2 promoter sequence contains two ABRE and one ERE in the upstream region of the start codon. The VlMYBA2 promoter can be activated by both ABA (more effective) and ACC, whereas the VlMYBA1-2 promoter can be activated by ABA only. In sum, ABA can promote the coloring of Kyoho grape by the promotion of VlMYBA1-2/2 transcriptions via activating the response of their promoters to ABA, whereas ethylene only regulates VlMYBA2 through the response activation of its promoter to ACC which partially enhances the coloring. [ABSTRACT FROM AUTHOR]

To investigate the contribution of abscisic acid (ABA) in pear 'Gold Nijisseiki' during fruit ripening and under dehydration stress, two cDNAs (PpNCED1 and PpNCED2) which encode 9-cis-epoxycarotenoid dioxygenase (NCED) (a key enzyme in ABA biosynthesis), two cDNAs (PpCYP707A1 and PpCYP707A2) which encode 8'-hydroxylase (a key enzyme in the oxidative catabolism of ABA), one cDNA (PpACS3) which encodes 1-aminocyclopropane-1-carboxylic acid (ACC), and one cDNA (PpACO1) which encodes ACC oxidase involved in ethylene biosynthesis were cloned from 'Gold Nijisseiki' fruit. In the pulp, peel and seed, expressions of PpNCED1 and PpNCED2 rose in two stages which corresponded with the increase of ABA levels. The expression of PpCYP707A1 dramatically declined after 60-90 days after full bloom (DAFB) in contrast to the changes of ABA levels during this period, while PpCYP707A2 stayed low during the whole development of fruit. Application of exogenous ABA at 100 DAFB increased the soluble sugar content and the ethylene release but significantly decreased the titratable acid and chlorophyll contents in fruits. When fruits harvested at 100 DAFB were stored in the laboratory (25 °C, 50% relative humidity), the ABA content and the expressions of PpNCED1/2 and PpCYP707A1 in the pulp, peel and seed increased significantly, while ethylene reached its highest value after the maximum peak of ABA accompanied with the expressions of PpACS3 and PpACO1. In sum the endogenous ABA may play an important role in the fruit ripening and dehydration of pear 'Gold Nijisseiki' and the ABA level was regulated mainly by the dynamics of PpNCED1, PpNCED2 and PpCYP707A1 at the transcriptional level. [ABSTRACT FROM AUTHOR]

Abstract: Cucumber (Cucumis sativus L.), a kind of fruit usually harvested at the immature green stage, belongs to non-climacteric fruit. To investigate the contribution of abscisic acid (ABA) to cucumber fruit development and ripening, variation in ABA level was investigated and a peak in ABA level was found in pulp before fruit get fully ripe. To clarify this point further, exogenous ABA was applied to cucumber fruits at two different development stages. Results showed that ABA application at the turning stage promotes cucumber fruit ripening, while application at the immature green stage had inconspicuous effects. In addition, with the purpose of understanding the transcriptional regulation of ABA, two partial cDNAs of CsNCED1 and CsNCED2 encoding 9-cis-epoxycarotenoid dioxygenase (NCED), a key enzyme in ABA biosynthetic pathway; one partial cDNA of CsCYP707A1 for 8′-hydroxylase, a key enzyme in the oxidative catabolism of ABA and two partial cDNAs of CsBG1 and CsBG2 for β-glucosidase (BG) that hydrolyzes ABA glucose ester (ABA-GE) to release active ABA were cloned from cucumber. The DNA and deduced amino acid sequences of these obtained genes respectively showed high similarities to their homologous genes in other plants. Real-time PCR analysis revealed that ABA content may be regulated by its biosynthesis (CsNCEDs), catabolism (CsCYP707A1) and reactivation genes (CsBGs) at the transcriptional level during cucumber fruit development and ripening, in response to ABA application, dehydration and pollination, among which CsNCED1, CsCYP707A1 and CsBG1 were highly expressed in pulp and may play more important roles in regulating ABA metabolism. [Copyright &y& Elsevier]

Abstract: The aim of this study was to obtain new insights into the mechanisms that regulate endogenous abscisic acid (ABA) levels by β-glucosidase genes during the development of watermelons (Citrullus lanatus) and under drought stress conditions. In total, five cDNAs from watermelons were cloned by using reverse transcription-PCR (RT-PCR). They included three cDNAs (ClBG1, ClBG2 and ClBG3) homologous to those that encode β-glucosidase l that hydrolyzes the ABA glucose ester (ABA-GE) to release active ABA, ClNCED4, which encodes 9-cis-epoxycarotenoid dioxygenase (NCED), a key enzyme in ABA biosynthesis, and ClCYP707A1, encoding ABA 8′-hydroxylase. A BLAST homology search revealed that the sequences of cDNAs and the deduced amino acids of these genes showed a high degree of homology to comparable molecules of other plant species. During fruit development and ripening, the expressions of ClBG1, ClNCED4 and ClCYP707A1 were relatively low at an early stage, increased rapidly along with fruit ripening, and reached the highest levels at 27 days after full bloom (DAFB) at the harvest stage. This trend was consistent with the accumulation of ABA. The ClBG2 gene on the other hand was highly expressed at 5 DAFB, and then decreased gradually with fruit development. Unlike ClBG1 and ClBG2, the expression of ClBG3 was low at an early stage; its expression peak occurred at 15 DAFB and then declined to the lowest point. When watermelon seedlings were subjected to drought stress, expressions of ClBG1 and ClCYP707A1 were significantly down-regulated, while expressions of ClBG2 and ClNCED4 were up-regulated in the roots, stems and leaves. The expression of ClBG3 was down-regulated in root tissue, but was up-regulated in stems and leaves. In conclusion, endogenous ABA content was modulated by a dynamic balance between biosynthesis and catabolism regulated by ClNCED4, ClCYP707A1 and ClBGs during development and under drought stress condition. It seems likely that β-glucosidase genes are important for this regulation process. [Copyright &y& Elsevier]