Phytochrome Regulates Gibberellin Biosynthesis during Germination of Photoblastic Lettuce Seeds

Toyomasu, Tomonobu; Kawaide, Hiroshi; Mitsuhashi, Wataru; Inoue, Yasunori; Kamiya, Yûji

doi:10.1104/pp.118.4.1517

Cited by 217 publications

(180 citation statements)

References 35 publications

(32 reference statements)

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“…For instance, light was shown to promote the germination of Arabidopsis and lettuce seeds by increasing their GA content via the induction GA 3b-hydroxylases (Toyomasu et al, 1998;Yamaguchi et al, 1998). Alabadí et al (2004) reported that both mutational and chemical disruption of GA synthesis can interfere with normal skotomorphogenesis and cause aberrant expression of light-regulated nuclear genes.…”

Section: Discussionmentioning

confidence: 99%

“…Remarkably, most lightresponsive genes of GA synthesis were also found to be under wavelength-or photoreceptor-specific control. In Arabidopsis, lettuce (Lactuca sativa), and pea (Pisum sativum), light was shown to regulate the expression of GA 3b-hydroxylase and GA 20-oxidase isoforms via either phytochrome-dependent or -independent mechanisms (Toyomasu et al, 1998;Yamaguchi et al, 1998;Ait-Ali et al, 1999;Jackson et al, 2000).…”

Section: Discussionmentioning

confidence: 99%

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Diurnal Regulation of the Brassinosteroid-Biosynthetic CPD Gene in Arabidopsis

et al. 2006

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Plant steroid hormones, brassinosteroids (BRs), are essential for normal photomorphogenesis. However, the mechanism by which light controls physiological functions via BRs is not well understood. Using transgenic plants carrying promoter-luciferase reporter gene fusions, we show that in Arabidopsis (Arabidopsis thaliana) the BR-biosynthetic CPD and CYP85A2 genes are under diurnal regulation. The complex diurnal expression profile of CPD is determined by dual, light-dependent, and circadian control. The severely decreased expression level of CPD in phytochrome-deficient background and the red light-specific induction in wildtype plants suggest that light regulation of CPD is primarily mediated by phytochrome signaling. The diurnal rhythmicity of CPD expression is maintained in brassinosteroid insensitive 1 transgenic seedlings, indicating that its transcriptional control is independent of hormonal feedback regulation. Diurnal changes in the expression of CPD and CYP85A2 are accompanied by changes of the endogenous BR content during the day, leading to brassinolide accumulation at the middle of the light phase. We also show that CPD expression is repressed in extended darkness in a BR feedback-dependent manner. In the dark the level of the bioactive hormone did not increase; therefore, our data strongly suggest that light also influences the sensitivity of plants to BRs.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Diurnal Regulation of the Brassinosteroid-Biosynthetic CPD Gene in Arabidopsis

et al. 2006

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“…9). Expression of GA3ox genes in lettuce and Arabidopsis is well known to be photoreversibly regulated by light through phytochrome (Toyomasu et al, 1998;Yamaguchi et al, 1998). Understanding the cross talk between light and temperature signals on the regulation of GA3ox gene expression may give us insight into how plants transduce multiple signals and how plants respond to complex environmental stimuli.…”

Section: Suppression Of Ga Synthesis Is Critical For Thermoinhibitionmentioning

confidence: 99%

“…Light signals mediated by phytochromes are critical environmental determinants for photoblastic seed germination (Borthwick et al, 1952;Shinomura et al, 1996). GA levels are regulated by phytochrome in lettuce and Arabidopsis seeds, in which genes encoding GA 3-oxidase (GA3ox) and GA 2-oxidase (GA2ox) are regulated in a photoreversible manner (Toyomasu et al, 1998;Yamaguchi et al, 1998). In Arabidopsis, GA3ox1 and GA3ox2 are up-regulated and GA2ox2 is down-regulated by red light, which promotes seed germination.…”

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confidence: 99%

High Temperature-Induced Abscisic Acid Biosynthesis and Its Role in the Inhibition of Gibberellin Action in Arabidopsis Seeds

et al. 2008

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Suppression of seed germination at supraoptimal high temperature (thermoinhibiton) during summer is crucial for Arabidopsis (Arabidopsis thaliana) to establish vegetative and reproductive growth in appropriate seasons. Abscisic acid (ABA) and gibberellins (GAs) are well known to be involved in germination control, but it remains unknown how these hormone actions (metabolism and responsiveness) are altered at high temperature. Here, we show that ABA levels in imbibed seeds are elevated at high temperature and that this increase is correlated with up-regulation of the zeaxanthin epoxidase gene ABA1/ZEP and three 9-cis-epoxycarotenoid dioxygenase genes, NCED2, NCED5, and NCED9. Reverse-genetic studies show that NCED9 plays a major and NCED5 and NCED2 play relatively minor roles in high temperature-induced ABA synthesis and germination inhibition. We also show that bioactive GAs stay at low levels at high temperature, presumably through suppression of GA 20-oxidase genes, GA20ox1, GA20ox2, and GA20ox3, and GA 3-oxidase genes, GA3ox1 and GA3ox2. Thermoinhibition-tolerant germination of loss-of-function mutants of GA negative regulators, SPINDLY (SPY) and RGL2, suggests that repression of GA signaling is required for thermoinibition. Interestingly, ABA-deficient aba2-2 mutant seeds show significant expression of GA synthesis genes and repression of SPY expression even at high temperature. In addition, the thermoinhibition-resistant germination phenotype of aba2-1 seeds is suppressed by a GA biosynthesis inhibitor, paclobutrazol. We conclude that high temperature stimulates ABA synthesis and represses GA synthesis and signaling through the action of ABA in Arabidopsis seeds.

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“…GA biosynthesis de novo is a prerequisite for germination because inhibitors of GA biosynthesis applied during imbibition effectively inhibit the process (Nambara et al, 1991;Derkx and Karssen, 1993). Arabidopsis seeds have a very low germination rate in the dark, while both light and cold promote seed germination, at least partially by stimulating GA biosynthesis (Derkx and Karssen, 1994;Toyomasu et al, 1998;Yamaguchi et al, 1998;Yamauchi et al, 2004). Furthermore, light and cold each have been shown to reduce expression of GA2ox2 (Yamauchi et al, 2004;Oh et al, 2006).…”

Section: Seed Germinationmentioning

confidence: 99%

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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Phytochrome Regulates Gibberellin Biosynthesis during Germination of Photoblastic Lettuce Seeds

Cited by 217 publications

References 35 publications

Diurnal Regulation of the Brassinosteroid-Biosynthetic CPD Gene in Arabidopsis

Diurnal Regulation of the Brassinosteroid-Biosynthetic CPD Gene in Arabidopsis

High Temperature-Induced Abscisic Acid Biosynthesis and Its Role in the Inhibition of Gibberellin Action in Arabidopsis Seeds

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

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