Gibberellin homeostasis in tobacco [Nicotiana tabacum] is regulated by gibberellin metabolism genes with different gibberellin sensitivity

• Published in: Plant and cell physiology Vol. 49; no. 5; pp. 679 - 690
• Main Authors: Gallego Giraldo, L.(Universidad Politecnica de Valencia (Spain)), Ubeda Tomas, S, Gisbert, C, Garcia Martinez, J.L, Moritz, T, Lopez Diaz, I
• Format: Journal Article
• Language: English
• Published: Japan Oxford University Press 01.05.2008; Oxford Publishing Limited (England)
• Subjects: ACIDE GIBBERELLIQUE; ACIDO GIBERELICO; Biosynthesis; catabolism; cell physiology; Feed-back; GENE; Gene Expression Regulation, Plant - drug effects; GENES; Genes, Plant; GIBBERELLIC ACID; Gibberellin; gibberellins; Gibberellins - metabolism; Gibberellins - pharmacology; growth and development; HOMEOSTASIE; HOMEOSTASIS; Homeostasis - drug effects; Homozygote; Hybridization, Genetic - drug effects; hybrids; Hypocotyl - drug effects; Inactivation; METABOLISM; METABOLISME; METABOLISMO; Mixed Function Oxygenases - genetics; Nicotiana - drug effects; Nicotiana - enzymology; Nicotiana - genetics; Nicotiana - metabolism; NICOTIANA TABACUM; Over-expression; Oxidation-Reduction - drug effects; Phenotype; Pisum sativum - drug effects; Pisum sativum - enzymology; PLANT GROWTH SUBSTANCES; plant hormones; Plant Proteins - genetics; Plant Proteins - metabolism; Plants, Genetically Modified; Regulation; RNA, Messenger - genetics; RNA, Messenger - metabolism; SUBSTANCE DE CROISSANCE VEGETALE; SUSTANCIAS DE CRECIMIENTO VEGETAL; TABAC; TABACO; TOBACCO; Transcription, Genetic - drug effects; Transgenic plants; Homeostasis; Feed-back; Gibberellin; Regulation; Over-expression
• ISSN: 0032-0781; 1471-9053; 1471-9053
• DOI: 10.1093/pcp/pcn042

Gibberellins are phytohormones that regulate growth and development of plants. Gibberellin homeostasis is maintained by feedback regulation of gibberellin metabolism genes. To understand this regulation, we manipulated the gibberellin pathway in tobacco and studied its effects on the morphological phenotype, gibberellin levels and the expression of endogenous gibberellin metabolism genes. The overexpression of a gibberellin 3-oxidase (biosynthesis gene) in tobacco (3ox-OE) induced slight variations in phenotype and active GA1 levels, but we also found an increase in GA8 levels (GA1 inactivation product) and a conspicuous induction of gibberellin 2-oxidases (catabolism genes; NtGA2ox3 and -5), suggesting an important role for these particular genes in the control of gibberellin homeostasis. The effect of simultaneous overexpression of two biosynthesis genes, a gibberellin 3-oxidase and a gibberellin 20-oxidase (20ox/3ox-OE), on phenotype and gibberellin content suggests that gibberellin 3-oxidases are non-limiting enzymes in tobacco, even in a 20ox-OE background. Moreover, the expression analysis of gibberellin metabolism genes in transgenic plants (3ox-OE, 20ox-OE and hybrid 3ox/20ox-OE), and in response to application of different GA1 concentrations, showed genes with different gibberellin sensitivity. Gibberellin biosynthesis genes (NtGA20ox1 and NtGA3ox1) are negatively feedback regulated mainly by high gibberellin levels. In contrast, gibberellin catabolism genes which are subject to positive feedback regulation are sensitive to high (NtGA2ox1) or to low (NtGA2ox3 and -5) gibberellin concentrations. These two last GA2ox genes seem to play a predominant role in gibberellin homeostasis under mild gibberellin variations, but not under large gibberellin changes, where the biosynthesis genes GA20ox and GA3ox may be more important.