Publications (11) View all
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Article: SEPALLATA1/2-suppressed mature apples have low ethylene, high auxin and reduced transcription of ripening-related genes.
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ABSTRACT: Fruit ripening is an important developmental trait in fleshy fruits, making the fruit palatable for seed dispersers. In some fruit species, there is a strong association between auxin concentrations and fruit ripening. We investigated the relationship between auxin concentrations and the onset of ethylene-related ripening in Malus × domestica (apples) at both the hormone and transcriptome levels. Transgenic apples suppressed for the SEPALLATA1/2 (SEP1/2) class of gene (MADS8/9) that showed severely reduced ripening were compared with untransformed control apples. In each apple type, free indole-3-acetic acid (IAA) concentrations were measured during early ripening. The changes observed in auxin were assessed in light of global changes in gene expression. It was found that mature MADS8/9-suppressed apples had a higher concentration of free IAA. This was associated with increased expression of the auxin biosynthetic genes in the indole-3-acetamide pathway. Additionally, in the MADS8/9-suppressed apples, there was less expression of the GH3 auxin-conjugating enzymes. A number of genes involved in the auxin-regulated transcription (AUX/IAA and ARF classes of genes) were also observed to change in expression, suggesting a mechanism for signal transduction at the start of ripening. The delay in ripening observed in MADS8/9-suppressed apples may be partly due to high auxin concentrations. We propose that, to achieve low auxin associated with fruit maturation, the auxin homeostasis is controlled in a two-pronged manner: (i) by the reduction in biosynthesis and (ii) by an increase in auxin conjugation. This is associated with the change in expression of auxin-signalling genes and the up-regulation of ripening-related genes.AoB plants. 01/2013; 5:pls047. -
Article: Apple SEPALLATA1/2-like genes control fruit flesh development and ripening.
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ABSTRACT: Flowering plants have utilised different floral structures to develop flesh tissue in fruits. Here we show that in the fleshy fruit apple (Malus x domestica), suppression of the homeologous SEPALLATA1/2 (SEP1/2)-like genes, MADS8 and MADS9, leads to sepaloid petals and greatly reduced fruit flesh. Immunolabelling of cell wall epitopes and differential staining shows that the developing hypanthium (from which the apple flesh develops) of MADS8/9 suppressed apple flowers lacks a tissue layer, and the remnant flesh tissue of fully developed apples has considerably smaller cells. From these observations it is proposed that MADS8 and MADS9 control the development of discrete zones within the hypanthium tissue, and therefore fruit flesh, and also act as foundations for different floral organ development. At fruit maturity the MADS8/9 suppressed apples do not ripen, both in terms of developmentally controlled ripening characters, such as starch degradation, and in ethylene-modulated ripening traits. Transient assays suggest that, like the RIN gene in tomato, the MADS9 gene acts as a transcriptional activator of the ethylene biosynthesis enzyme ACC SYNTHASE-1 (ACS1). By having a single class of genes that regulate both flesh-formation and ripening, plants possess a powerful evolutionary tool for controlling two critical aspects of fleshy fruit development. © 2012 © 2012 The New Zealand Institute for Plant and Food Research limited The Plant Journal © 2012 Blackwell Publishing Ltd.The Plant Journal 12/2012; · 6.16 Impact Factor -
Article: Fruit development of the diploid kiwifruit, Actinidia chinensis 'Hort16A'.
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ABSTRACT: With the advent of high throughput genomic tools, it is now possible to undertake detailed molecular studies of individual species outside traditional model organisms. Combined with a good understanding of physiological processes, these tools allow researchers to explore natural diversity, giving a better understanding of biological mechanisms. Here a detailed study of fruit development from anthesis through to fruit senescence is presented for a non-model organism, kiwifruit, Actinidia chinensis ('Hort16A'). Consistent with previous studies, it was found that many aspects of fruit morphology, growth and development are similar to those of the model fruit tomato, except for a striking difference in fruit ripening progression. The early stages of fruit ripening occur as the fruit is still growing, and many ripening events are not associated with autocatalytic ethylene production (historically associated with respiratory climacteric). Autocatalytic ethylene is produced late in the ripening process as the fruit begins to senesce. By aligning A. chinensis fruit development to a phenological scale, this study provides a reference framework for subsequent physiological and genomic studies, and will allow cross comparison across fruit species, leading to a greater understanding of the diversity of fruits found across the plant kingdom.BMC Plant Biology 12/2011; 11:182. · 3.45 Impact Factor -
Article: Analysis of a post-translational steroid induction system for GIGANTEA in Arabidopsis.
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ABSTRACT: To investigate the link between the flowering time gene GIGANTEA (GI) and downstream genes, an inducible GI system was developed in Arabidopsis thaliana L. Heynh. Transgenic Arabidopsis plant lines were generated with a steroid-inducible post-translational control system for GI. The gene expression construct consisted of the coding region of the GI protein fused to that of the ligand binding domain of the rat glucocorticoid receptor (GR). This fusion gene was expressed from the constitutive cauliflower mosaic virus 35S promoter and was introduced into plants carrying the gi-2 mutation. Application of the steroid dexamethasone (DEX) was expected to result in activation of the GI-GR protein and its relocation from the cytoplasm to the nucleus. Application of DEX to the transgenic plant lines rescued the late flowering phenotype conferred by the gi-2 mutation. However, despite their delayed flowering in the absence of steroid, the transgenic lines expressed predicted GI downstream genes such as CONSTANS (CO) to relatively high levels. Nevertheless, increased CO and FLOWERING LOCUS T (FT) transcript accumulation was observed in transgenic plants within 8 h of DEX treatment compared to controls which was consistent with promotion of flowering by DEX. Unlike CO and FT, there was no change in the abundance of transcript of two other putative GI downstream genes HEME ACTIVATOR PROTEIN 3A (HAP3A) or TIMING OF CHLOROPHYLL A/B BINDING PROTEIN 1 (TOC1) after DEX application. The post-translational activation of GI and promotion of flowering by steroid application supports a nuclear role for GI in the floral transition. Known downstream flowering time genes CO and FT were elevated by DEX treatment, but not other proposed targets HAP3A and TOC1, indicating that the expression of these genes may be less directly regulated by GI.BMC Plant Biology 11/2009; 9:141. · 3.45 Impact Factor -
Article: Analysis of a post-translational steroid induction system for GIGANTEA in Arabidopsis
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ABSTRACT: Abstract Background To investigate the link between the flowering time gene GIGANTEA ( GI ) and downstream genes, an inducible GI system was developed in Arabidopsis thaliana L. Heynh. Transgenic Arabidopsis plant lines were generated with a steroid-inducible post-translational control system for GI. The gene expression construct consisted of the coding region of the GI protein fused to that of the ligand binding domain of the rat glucocorticoid receptor (GR). This fusion gene was expressed from the constitutive cauliflower mosaic virus 35S promoter and was introduced into plants carrying the gi-2 mutation. Application of the steroid dexamethasone (DEX) was expected to result in activation of the GI-GR protein and its relocation from the cytoplasm to the nucleus. Results Application of DEX to the transgenic plant lines rescued the late flowering phenotype conferred by the gi-2 mutation. However, despite their delayed flowering in the absence of steroid, the transgenic lines expressed predicted GI downstream genes such as CONSTANS (CO) to relatively high levels. Nevertheless, increased CO and FLOWERING LOCUS T ( FT ) transcript accumulation was observed in transgenic plants within 8 h of DEX treatment compared to controls which was consistent with promotion of flowering by DEX. Unlike CO and FT , there was no change in the abundance of transcript of two other putative GI downstream genes HEME ACTIVATOR PROTEIN 3A ( HAP3A ) or TIMING OF CHLOROPHYLL A/B BINDING PROTEIN 1 ( TOC1 ) after DEX application. Conclusion The post-translational activation of GI and promotion of flowering by steroid application supports a nuclear role for GI in the floral transition. Known downstream flowering time genes CO and FT were elevated by DEX treatment, but not other proposed targets HAP3A and TOC1 , indicating that the expression of these genes may be less directly regulated by GI.BMC Plant Biology. 01/2009;
