Contribution of Gibberellins to the Formation of Arabidopsis Seed Coat Through Starch Degradation

Kim, Young-Cheon; Nakajima, Miki; Nakayama, Akira; Yamaguchi, Isomaro

doi:10.1093/pcp/pci141

Cited by 55 publications

(69 citation statements)

References 32 publications

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“…These results contrast with observations that GA 2b-hydroxylase activity is abundant in seeds of many plants during the later stages of maturation, particularly in legume seeds, which accumulate large amounts of 2b-hydroxylated GAs (Durley et al, 1971;Frydman et al, 1974;Albone et al, 1984). Arabidopsis, which also has high levels of expression of GA biosynthetic genes in the developing seed (Kim et al, 2005;Schmid et al, 2005), must therefore have alternative mechanisms of GA inactivation, such as methylation (Varbanova et al, 2007), in these tissues.…”

Section: Discussion C 19 -Ga 2-oxidase Activity In Arabidopsiscontrasting

confidence: 87%

Genetic Analysis Reveals That C19-GA 2-Oxidation Is a Major Gibberellin Inactivation Pathway inArabidopsis

et al. 2008

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Bioactive hormone concentrations are regulated both at the level of hormone synthesis and through controlled inactivation. Based on the ubiquitous presence of 2β-hydroxylated gibberellins (GAs), a major inactivating pathway for the plant hormone GA seems to be via GA 2-oxidation. In this study, we used various approaches to determine the role of C19-GA 2-oxidation in regulating GA concentration and GA-responsive plant growth and development. We show that Arabidopsis thaliana has five C19-GA 2-oxidases, transcripts for one or more of which are present in all organs and at all stages of development examined. Expression of four of the five genes is subject to feed-forward regulation. By knocking out all five Arabidopsis C19-GA 2-oxidases, we show that C19-GA 2-oxidation limits bioactive GA content and regulates plant development at various stages during the plant life cycle: C19-GA 2-oxidases prevent seed germination in the absence of light and cold stimuli, delay the vegetative and floral phase transitions, limit the number of flowers produced per inflorescence, and suppress elongation of the pistil prior to fertilization. Under GA-limited conditions, further roles are revealed, such as limiting elongation of the main stem and side shoots. We conclude that C19-GA 2-oxidation is a major GA inactivation pathway regulating development in Arabidopsis.

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Section: Discussion C 19 -Ga 2-oxidase Activity In Arabidopsiscontrasting

confidence: 87%

Genetic Analysis Reveals That C19-GA 2-Oxidation Is a Major Gibberellin Inactivation Pathway inArabidopsis

et al. 2008

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“…A plausible mechanism for the latter effect may consist of the formation of the seed coat or testa. GAs are required for the normal formation of this structure through starch degradation (Kim et al, 2005), and the seed coat is very important to protect the embryo from stresses during storage (Clerkx et al, 2004;Rajjou and Debeaujon, 2008). The maternal effect observed during reciprocal crosses between wild-type and ATHB25-overexpressing plants suggests that a plausible mechanism for this transcription factor to increase seed longevity is that, by increasing GA synthesis, it reinforces the seed coat.…”

Section: Discussionmentioning

confidence: 99%

“…Other portions of the seed coat that could play a role in seed coat reinforcement and seed longevity are the secondary cell walls of the epidermal mucilage cells (columellae) and the subepidermal palisade cells (Debeaujon et al, 2000;Rajjou and Debeaujon, 2008). It is plausible that during starch degradation promoted by GA, these walls are also made thicker, in addition to the increased mucilage production (Kim et al, 2005). It is also possible that altered GA production could increase proanthocyanidin synthesis in the endothelial layer of the seed coat, which has also been implicated in seed longevity (Rajjou and Debeaujon, 2008).…”

Section: Discussionmentioning

confidence: 99%

“…As GAs regulate growth and development (Swain and Singh, 2005), the alternative mechanism could be that GAs promote the formation of some parts of the seed coat, an important structure for seed longevity (Debeaujon et al, 2000;Clerkx et al, 2004;Rajjou and Debeaujon, 2008). Kim et al (2005) have reported that the seed coat of a knockout mutant in the GA3OX4 gene (encoding a seed-specific enzyme of GA biosynthesis) is distorted, with abnormal cell shape and reduced mucilage. The Table II.…”

Section: Seed Longevity Dependent On Ga Correlates With Mucilage Formmentioning

confidence: 99%

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ARABIDOPSIS THALIANA HOMEOBOX25 Uncovers a Role for Gibberellins in Seed Longevity

et al. 2013

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Seed longevity is crucial for agriculture and plant genetic diversity, but it is limited by cellular damage during storage. Seeds are protected against aging by cellular defenses and by structures such as the seed coat. We have screened an activation-tagging mutant collection of Arabidopsis (Arabidopsis thaliana) and selected four dominant mutants with improved seed longevity (isl1-1D to isl4-1D) under both natural and accelerated aging conditions. In the isl1-1D mutant, characterized in this work, overexpression of the transcription factor ARABIDOPSIS THALIANA HOMEOBOX25 (ATHB25; At5g65410) increases the expression of GIBBERELLIC ACID3-OXIDASE2, encoding a gibberellin (GA) biosynthetic enzyme, and the levels of GA 1 and GA 4 are higher (3.2-and 1.4-fold, respectively) in the mutant than in the wild type. The morphological and seed longevity phenotypes of the athb25-1D mutant were recapitulated in transgenic plants with moderate (4-to 6-fold) overexpression of ATHB25. Simultaneous knockdown of ATHB25, ATHB22, and ATHB31 expression decreases seed longevity, as does loss of ATHB25 and ATHB22 function in a double mutant line. Seeds from wild-type plants treated with GA and from a quintuple DELLA mutant (with constitutive GA signaling) are more tolerant to aging, providing additional evidence for a role of GA in seed longevity. A correlation was observed in several genotypes between seed longevity and mucilage formation at the seed surface, suggesting that GA may act by reinforcing the seed coat. This mechanism was supported by the observation of a maternal effect in reciprocal crosses between the wild type and the athb25-1D mutant.

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“…Hormones are also involved in mucilage production. Mutations in two genes, GIBBERELLIN3-OXIDASE4 (GA3OX4; Kim et al, 2005) and ABSCISIC ACID DEFICIENT1 (ABA1; Karssen et al, 1983), related to GA 3 and abscisic acid metabolism, respectively, also affect mucilage synthesis.…”

mentioning

confidence: 99%

GALACTURONOSYLTRANSFERASE-LIKE5 Is Involved in the Production of Arabidopsis Seed Coat Mucilage

et al. 2013

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The function of a putative galacturonosyltransferase from Arabidopsis (Arabidopsis thaliana; At1g02720; GALACTURONOSYLTRANSFERASE-LIKE5 [AtGATL5]) was studied using a combination of molecular genetic, chemical, and immunological approaches. AtGATL5 is expressed in all plant tissues, with highest expression levels in siliques 7 DPA. Furthermore, its expression is positively regulated by several transcription factors that are known to regulate seed coat mucilage production. AtGATL5 is localized in both endoplasmic reticulum and Golgi, in comparison with marker proteins resident to these subcellular compartments. A transfer DNA insertion in the AtGATL5 gene generates seed coat epidermal cell defects both in mucilage synthesis and cell adhesion. Transformation of atgatl5-1 mutants with the wild-type AtGATL5 gene results in the complementation of all morphological phenotypes. Compositional analyses of the mucilage isolated from the atgatl5-1 mutant demonstrated that galacturonic acid and rhamnose contents are decreased significantly in atgatl5-1 compared with wild-type mucilage. No changes in structure were observed between soluble mucilage isolated from wild-type and mutant seeds, except that the molecular weight of the mutant mucilage increased 63% compared with that of the wild type. These data provide evidence that AtGATL5 might function in the regulation of the final size of the mucilage rhamnogalacturonan I.

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Contribution of Gibberellins to the Formation of Arabidopsis Seed Coat Through Starch Degradation

Cited by 55 publications

References 32 publications

Genetic Analysis Reveals That C19-GA 2-Oxidation Is a Major Gibberellin Inactivation Pathway inArabidopsis

Genetic Analysis Reveals That C19-GA 2-Oxidation Is a Major Gibberellin Inactivation Pathway inArabidopsis

ARABIDOPSIS THALIANA HOMEOBOX25 Uncovers a Role for Gibberellins in Seed Longevity

GALACTURONOSYLTRANSFERASE-LIKE5 Is Involved in the Production of Arabidopsis Seed Coat Mucilage

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