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.

Indução, análises morfológicas e ultraestruturais de calos de maracujazeiro nativo

“…Células podem-se tornar competentes para embriogênese somática, desde que a interação entre fatores endógenos e exógenos, como a concentração e o tipo de regulador de crescimento utilizado, esteja balanceada, desencadeando uma série de eventos moleculares que podem afetar a expressão do gene e determinar a diferenciação de embriões somáticos (Nolan et al, 2014). A adição de auxinas exógenas ao meio de cultura pode aumentar a totipotência de células com habilidade para proliferar e regenerar embriões somáticos (Garcia et al, 2011).…”

Effects of abscisic acid and an osmoticum on the maturation, starch accumulation and germination of Picea spp. somatic embryos

“…The development of somatic embryos of various coniferous tree species is affected mainly by the concentrations of ABA, sucrose or Phytagel (osmoticum) in the maturation medium Iraqi and Tremblay 2001;Teixteira da Silva and Malabadi 2012;Nolan et al 2014). The concentrations of these components may also be crucial for the further development of the embryos into plants.…”

Protocols for Obtaining Zygotic and Somatic Embryos for Studying the Regulation of Early Embryo Development in the Model Legume <em>Medicago truncatula</em>

“…In the legume model M. truncatula, the seed line Jemalong 2HA (2HA) has been developed from the parent Jemalong to have high rates of somatic embryogenesis 13 . The number of embryos produced has recently been substantively increased by adding both gibberellic acid (GA) and abscisic acid (ABA) to the long established medium 14 . In this case GA and ABA act synergistically, which is unusual given that GA and ABA usually act antagonistically 14 .…”

“…The number of embryos produced has recently been substantively increased by adding both gibberellic acid (GA) and abscisic acid (ABA) to the long established medium 14 . In this case GA and ABA act synergistically, which is unusual given that GA and ABA usually act antagonistically 14 . The embryos produced from callus develop on the surface which allows the stage of embryogenesis to be readily determined visually and readily harvested.…”