title: An unusual abscisic acid and gibberellic acid synergism increases somatic embryogenesis, facilitates its genetic analysis and improves transformation in Medicago truncatula.
abstract: Somatic embryogenesis (SE) can be readily induced in leaf explants of the Jemalong 2HA genotype of the model legume Medicago truncatula by auxin and cytokinin, but rarely in wild-type Jemalong. Gibberellic acid (GA), a hormone not included in the medium, appears to act in Arabidopsis as a repressor of the embryonic state such that low ABA (abscisic acid): GA ratios will inhibit SE. It was important to evaluate the GA effect in M. truncatula in order to formulate generic SE mechanisms, given the Arabidopsis information. It was surprising to find that low ABA:GA ratios in M. truncatula acted synergistically to stimulate SE. The unusual synergism between GA and ABA in inducing SE has utility in improving SE for regeneration and transformation in M. truncatula. Expression of genes previously shown to be important in M. truncatula SE was not increased. In investigating genes previously studied in GA investigations of Arabidopsis SE, there was increased expression of GA2ox and decreased expression of PICKLE, a negative regulator of SE in Arabidopsis. We suggest that in M. truncatula there are different ABA:GA ratios required for down-regulating the PICKLE gene, a repressor of the embryonic state. In M. truncatula it is a low ABA:GA ratio while in Arabidopsis it is a high ABA:GA ratio. In different species the expression of key genes is probably related to differences in how the hormone networks optimise their expression.
authors.affiliation: School of Environmental and Life Sciences, The University of Newcastle, Callaghan, New South Wales, Australia.
authors.forename: Kim E
authors.initials: KE
authors.lastname: Nolan
authors.affiliation: School of Environmental and Life Sciences, The University of Newcastle, Callaghan, New South Wales, Australia.
authors.forename: Youhong
authors.initials: Y
authors.lastname: Song
authors.affiliation: School of Environmental and Life Sciences, The University of Newcastle, Callaghan, New South Wales, Australia.
authors.forename: Siyang
authors.initials: S
authors.lastname: Liao
authors.affiliation: School of Environmental and Life Sciences, The University of Newcastle, Callaghan, New South Wales, Australia.
authors.forename: Nasir A
authors.initials: NA
authors.lastname: Saeed
authors.affiliation: School of Environmental and Life Sciences, The University of Newcastle, Callaghan, New South Wales, Australia.
authors.forename: Xiyi
authors.initials: X
authors.lastname: Zhang
authors.affiliation: School of Environmental and Life Sciences, The University of Newcastle, Callaghan, New South Wales, Australia.
authors.forename: Ray J
authors.initials: RJ
authors.lastname: Rose
mesh_terms: D000040:Abscisic Acid / Q000494:pharmacology*; D004357:Drug Synergism; D015870:Gene Expression; D017343:Genes, Plant; D005875:Gibberellins / Q000494:pharmacology*; D046913:Medicago truncatula / Q000502:physiology*; D010937:Plant Growth Regulators / Q000494:pharmacology*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D058439:Plant Somatic Embryogenesis Techniques; D014170:Transformation, Genetic
chemical_list: D005875:Gibberellins; D010937:Plant Growth Regulators; D010940:Plant Proteins; D000040:Abscisic Acid; C007842:gibberellic acid