The plant hormone abscisic acid (ABA) has been suggested to play a role in fruit development, but supporting genetic evidence has been lacking. Here, we report that ABA promotes strawberry (Fragaria ananassa) fruit ripening. Using a newly established Tobacco rattle virus-induced gene silencing technique in strawberry fruit, the expression of a 9-cis-epoxycarotenoid dioxygenase gene (FaNCED1), which is key to ABA biosynthesis, was down-regulated, resulting in a significant decrease in ABA levels and uncolored fruits. Interestingly, a similar uncolored phenotype was observed in the transgenic RNA interference (RNAi) fruits, in which the expression of a putative ABA receptor gene encoding the magnesium chelatase H subunit (FaCHLH/ABAR) was down-regulated by virus-induced gene silencing. More importantly, the uncolored phenotype of the FaNCED1-downregulated RNAi fruits could be rescued by exogenous ABA, but the ABA treatment could not reverse the uncolored phenotype of the FaCHLH/ABAR-down-regulated RNAi fruits. We observed that down-regulation of the FaCHLH/ABAR gene in the RNAi fruit altered both ABA levels and sugar content as well as a set of ABA-and/or sugar-responsive genes. Additionally, we showed that exogenous sugars, particularly sucrose, can significantly promote ripening while stimulating ABA accumulation. These data provide evidence that ABA is a signal molecule that promotes strawberry ripening and that the putative ABA receptor, FaCHLH/ABAR, is a positive regulator of ripening in response to ABA.

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Although the plant hormone abscisic acid (ABA) has been suggested to play a role in the ripening of non-climatic fruit, direct genetic/molecular evidence is lacking. In the present study, a strawberry gene homologous to the Arabidopsis ABA receptor gene PYR1, named FaPYR1, was isolated and characterized. The 627 bp cDNA includes an intact open reading frame that encodes a deduced protein of 208 amino acids, in which putative conserved domains were detected by homology analysis. Using tobacco rattle virus-induced gene silencing (VIGS), the FaPYR1 gene was silenced in strawberry fruit. Down-regulation of the FaPYR1 gene not only significantly delayed fruit ripening, but also markedly altered ABA content, ABA sensitivity, and a set of ABA-responsive gene transcripts, including ABI1 and SnRK2. Furthermore, the loss of red colouring in FaPYR1 RNAi (RNA interference) fruits could not be rescued by exogenously applied ABA, which could promote the ripening of wild-type fruits. Collectively, these results demonstrate that the putative ABA receptor FaPYR1 acts as a positive regulator in strawberry fruit ripening. It was also revealed that the application of the VIGS technique in strawberry fruit could be used as a novel tool for studying strawberry fruit development.

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High-amylose maize starch (HAM) is a common source material to make resistant starch with its high content of amylose (>70%). In the current investigation, the self-assembly of amylose in the presence of bioactive tea polyphenols (TPLs) and resulting slow digestion property of starch were explored. The experimental results using a mouse model showed a slow digestion property can be achieved with an extended and moderate glycemic response to HAM starch cocooked with TPLs. Further studies using a dilute aqueous amylose solution (0.1%, w/v) revealed an increased hydrodynamic radius of amylose molecules, indicating that TPLs could bridge them together, leading to increased molecular sizes. On the other hand, the bound TPLs interrupted the normal process of amylose recrystallizaiton evidenced by a decreased viscosity and storage modulus (G') of HAM (5%) gel, a rough surface of the cross-section of HAM film, and decreased short-range orders examined by Fourier transform infrared spectral analysis. Single-step degradation curves in the thermal gravimetric profile demonstrated the existence of a self-assembled amylose-TPL complex, which is mainly formed through hydrogen bonding interaction according to the results of iodine binding and X-ray powder diffraction analysis. Collectively, the amylose-TPL complexation influences the normal self-assembling process of amylose, leading to a low-ordered crystalline structure, which is the basis for TPLs' function in modulating the digestion property of HAM starch to produce a slowly digestible starch material that is beneficial to postprandial glycemic control and related health effects.

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On basis of fruit differential respiration and ethylene effects, climacteric and non-climacteric fruits have been classically defined. Over the past decades, the molecular mechanisms of climacteric fruit ripening were abundantly described and found to focus on ethylene perception and signaling transduction. In contrast, until our most recent breakthroughs, much progress has been made toward understanding the signaling perception and transduction mechanisms for abscisic acid (ABA) in strawberry, a model for non-climacteric fruit ripening. Our reports not only have provided several lines of strong evidences for ABA-regulated ripening of strawberry fruit, but also have demonstrated that homology proteins of Arabidopsis ABA receptors, including PYR/PYL/RCAR and ABAR/CHLH, act as positive regulators of ripening in response to ABA. These receptors also trigger a set of ABA downstream signaling components, and determine significant changes in the expression levels of both sugar and pigment metabolismrelated genes that are closely associated with ripening. Soluble sugars, especially sucrose, may act as a signal molecular to trigger ABA accumulation through an enzymatic action of 9-cis-epoxycarotenoid dioxygenase 1 (FaNCED1). This minireview offers an overview of these processes and also outlines the possible, molecular mechanisms for ABA in the regulation of strawberry fruit ripening through the ABA receptors. Abscisic acid perception and signaling transduction in strawberryA model for non-climacteric fruit ripening Our recent reports have provided strong evidences that ABA plays a crucial role in the regulation of ripening related-gene expression through ABA perception and signaling transduction in strawberry fruit.9,10 These and previous studies provide several lines of evidences that the interaction between sugar and ABA may be a core mechanism in regulation of the ripening of nonclimacteric fruits. ABA is Required for Strawberry Fruit RipeningAs a plant hormone, ABA not only plays a central role in the adaptation of plants to adverse conditions, but also regulates various aspects of plant growth and development, such as seed dormancy, seedling growth and fruit development.11-13 Notably, ABA is considered to play even more important roles than that of ethylene in fruit maturation and senescence.14 Ripening of strawberry (Fragaria x ananassa), a model for non-climacteric fruits, is previously reported to be promoted by ABA. 15 In accordance with this notion, our recent reports also showed that exogenous ABA can significantly accelerate strawberry fruit ripening, and a remarkable decrease in ABA content that results from the downregulation of the transcripts of a 9-cis-epoxycarotenoid dioxygenase gene (FaNCED1) by virus-induced gene silencing (VIGS), can significantly retard the ripening process.9 To our knowledge, this is the first direct molecular evidence on the requirement of ABA for strawberry fruit ripening.

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