Summary
Fleshy fruits are classically divided into climacteric and nonclimacteric types. It has long been thought that the ripening of climacteric and nonclimacteric fruits is regulated by ethylene and abscisic acid (ABA), respectively. Here, we report that sucrose functions as a signal in the ripening of strawberry (Fragaria × ananassa), a nonclimacteric fruit.
Pharmacological experiments, as well as gain‐ and loss‐of‐function studies, were performed to demonstrate the critical role of sucrose in the regulation of fruit ripening.
Fruit growth and development were closely correlated with a change in sucrose content. Exogenous sucrose and its nonmetabolizable analog, turanose, induced ABA accumulation in fruit and accelerated dramatically fruit ripening. A set of sucrose transporters, FaSUT1–7, was identified and characterized, among which FaSUT1 was found to be a major component responsible for sucrose accumulation during fruit development. RNA interference‐induced silencing of FaSUT1 led to a decrease in both sucrose and ABA content, and arrested fruit ripening. By contrast, overexpression of FaSUT1 led to an increase in both sucrose and ABA content, and accelerated fruit ripening.
In conclusion, this study demonstrates that sucrose is an important signal in the regulation of strawberry fruit ripening.
Apple leaf spot caused by the f. sp (ALT1) fungus is one of the most devastating diseases of apple ( × ). We identified a hairpin RNA () named that produces small RNAs and is induced by ALT1 infection in 'Golden Delicious' apple. produces mdm-siR277-1 and mdm-siR277-2, which target five resistance () genes that are expressed at high levels in resistant apple variety 'Hanfu' and at low levels in susceptible variety 'Golden Delicious' following ALT1 infection. was strongly induced in 'Golden Delicious' but not 'Hanfu' following ALT1 inoculation. promoter activity was much stronger in inoculated 'Golden Delicious' versus 'Hanfu'. We identified a single-nucleotide polymorphism (SNP) in the promoter region between 'Golden Delicious' () and 'Hanfu' (). The transcription factor MdWHy binds to , but not to Transgenic 'GL-3' apple expressing was more susceptible to ALT1 infection than plants expressing due to induced mdm-siR277 accumulation and reduced expression of the five target genes. We confirmed that the SNP in is associated with leaf spot resistance by crossing. This SNP could be used as a marker to distinguish between apple varieties that are resistant or susceptible to leaf spot.
DNA methylation is an epigenetic modification essential for gene regulations in plants, but understanding on how it is involved in fruit development, especially in non-climacteric fleshy fruit, is limited. The diploid woodland strawberry (Fragaria vesca) is an important model for non-climacteric fruit crops. In this study, we identified DNA methyltransferase genes and demethylase genes in Fragaria vesca and other angiosperm species. In accordance with previous studies, our phylogenetic analyses of those DNA methylation modifiers support the clustering of those genes into several classes. Our data indicate that whole-genome duplications and tandem duplications contributed to the expansion of those DNA methylation modifiers in angiosperms. We have further demonstrated that some DNA methylase and demethylase genes reach their highest expression levels in strawberry fleshy fruits when turning from white to red, suggesting that DNA methylation might undergo a dramatic change at the onset of fleshy fruit-ripening process. In addition, we have observed that expression of some DNA demethylase genes increases in response to various abiotic stresses including heat, cold, drought and salinity. Collectively, our study indicates a regulatory role of DNA methylation in the turning stage of non-climacteric fleshy fruit and responses to environment stimuli, and would facilitate functional studies of DNA methylation in the growth and development of non-climacteric fruits.
The dirhodium(II) catalyst Rh2(esp)2 allows direct solvent-free allylic and benzylic oxidations by T-HYDRO with a remarkably low catalyst loading. This method is operationally simple and scalable at ambient temperature without the use of any additives. The high catalyst stability in these reactions may be attributed to a dirhodium(II,II) catalyst resting state, which is less prone to decomposition.
[reaction: see text] A practical highly diastereoselective synthesis of 1,2-diamines through carbon-carbon bond formation involving an ammonium ylide intermediate is reported for the first time. By treating methyl phenyldiazoacetate with arylamine and imine in the presence of dirhodium acetate, the erythro diastereomer of methyl 1,2-diaryl-1,2-diaminopropanoate is formed with stereochemical preferences greater than 10:1.
Dedicated to Professor Henri Brunner on the occasion of his 72nd birthday Chiral dirhodium(II) carboxamidates have high potential for enantioselective Lewis acid catalyzed reactions because they hold the Lewis base, which is activated for reaction, at the axial coordination site in close proximity to the ligand attachments for chiral differentiation. As has already been demonstrated for the hetero-Diels-Alder reaction (Scheme 1) [1,2] and for trimethylsilylketene/glyoxal cycloaddition, [3] the chiral environment around the axial coordination site strongly influences enantiocontrol and also pushes the product off the rhodium axial coordination site to provide turnover numbers (TON) as high as 10 000. However, the Lewis acidity for dirhodium(II) carboxamidates is low compared to that of many other catalysts for these reactions.[4] Suitable Diels-Alder, ene, and dipolar cycloaddition reactions, for example, show no catalytic activity with chiral dirhodium(II) carboxamidates, even with a,adifluoro analogues of the mepy and meaz catalysts that were developed to enhance Lewis acid association with Lewis bases.[5] We have prepared cationic Rh II /Rh III counterparts to the moderately active chiral dirhodium(II) carboxamidates to enhance the Lewis acidity of these chiral dirhodium catalysts. Cationic metal complexes are now commonly used to achieve rate and selectivity enhancements for those transformations suitable to catalysis by the cationic metal complex.[6] We anticipated that cationic chiral Rh II /Rh III compounds could increase the closeness of association of the catalyst with Lewis bases, increase the rate of reaction with selected substrates, and enhance enantiocontrol.Oxidation of dirhodium(II) (Rh 2 4+ ) compounds is well known ,[6] but their Rh 2 5+ counterparts have been produced in the presence of either a less labile ligand such as halide [7] or by using another transition metal such as Ag I , Ce IV , or Cu II for the oxidation, [6,8] none of which are amenable to the use of Rh 2 5+ complexes as catalysts without laborious separation or further catalyst manipulation. However, we have recently discovered that nitrosonium salts effect facile oxidation of dirhodium(II) carboxamidates at room temperature to form the corresponding Rh II /Rh III salts quantitatively, evolving nitric oxide in the process. These complexes exhibit a characteristic electronic absorption near 1000 cm À1 . A crystal structure for the bis(acetonitrile) complex of [Rh 2 {(4S)-meox} 4 ]BF 4 is shown in Figure 1.To test the ability of chiral Rh 2 5+ carboxamidates to enhance selectivity in Lewis acid catalyzed transformations we turned our attention to the hetero-Diels-Alder reaction and to [Rh 2 (mepy) 4 ] as the catalyst. As has been reported, [1a] the use of 1.0 mol % [Rh 2 (mepy) 4 ] with p-nitrobenzaldehyde and the Danishefsky diene (see Scheme 1) resulted in the corresponding hetero-Diels-Alder product (53 % yield) in 73 % ee; use of the corresponding Rh 2 5+ complex, [Rh 2 {(5S)-mepy} 4 ]BF 4 , produced the same product in 93 %...
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