Abstract
Ethylene is a plant hormone controlling physiological and developmental processes such as fruit maturation, hairy root formation, and leaf abscission. Its effect on regeneration systems, such as organogenesis and somatic embryogenesis (SE), has been studied, and progress in molecular biology techniques have contributed to unveiling the mechanisms behind its effects. The influence of ethylene on regeneration should not be overlooked. This compound affects regeneration differently, depending on the species, genotype, and explant. In some species, ethylene seems to revert recalcitrance in genotypes with low regeneration capacity. However, its effect is not additive, since in genotypes with high regeneration capacity this ability decreases in the presence of ethylene precursors, suggesting that regeneration is modulated by ethylene. Several lines of evidence have shown that the role of ethylene in regeneration is markedly connected to biotic and abiotic stresses as well as to hormonal-crosstalk, in particular with key regeneration hormones and growth regulators of the auxin and cytokinin families. Transcriptional factors of the ethylene response factor (ERF) family are regulated by ethylene and strongly connected to SE induction. Thus, an evident connection between ethylene, stress responses, and regeneration capacity is markedly established. In this review the effect of ethylene and the way it interacts with other players during organogenesis and somatic embryogenesis is discussed. Further studies on the regulation of ERF gene expression induced by ethylene during regeneration can contribute to new insights on the exact role of ethylene in these processes. A possible role in epigenetic modifications should be considered, since some ethylene signaling components are directly related to histone acetylation.
Highlights
Micropropagation has been studied and developed through the years, and is currently one of the best alternatives for large-scale propagation and conservation of a wide range of plant species [1]
The negative effect of both ETH and silver nitrate in the number of shoots per explant with shoots (%) in Solanum pennellii, ACC treatments enhanced this parameter. These results show that different genotypes have different responses and sensitivity to ethylene and/or its modulation, affecting its regeneration capacity
Experiments carried out during shoot regeneration in cotyledons of different Arabidopsis mutants (Table 2) showed that shoot regeneration decreased in ethylene insensitive mutants etr1-1 and ein2-1, whereas it increased in ethylene constitutive response mutants ctr1-1 and ctr1-12, and in ethylene overproducer mutant eto1-1, suggesting a positive role for ethylene on Arabidopsis organogenesis [126]
Summary
Micropropagation has been studied and developed through the years, and is currently one of the best alternatives for large-scale propagation and conservation of a wide range of plant species [1]. Carbon source, plant growth regulators (PGRs), gelling agents, pH, light, temperature, and the gaseous environment are the factors to take into consideration for the success of the different in vitro plant propagation and regeneration processes [1] Plant regeneration systems, such as organogenesis and somatic embryogenesis (SE) are well-known micropropagation processes based on plant cells pluripotency/totipotency. The presence of PGRs in the culture media—in particular, auxins and cytokinins—is required for the success of plant regeneration, since a balance between both hormones contributes to enhance the in vitro regenerative capacity of a myriad of plant species [3] While these PGRs are deliberately placed in the culture medium in a well-defined added concentration, and a dose–response assay can be evaluated, the role of gaseous compounds, such as the hormone ethylene, is more difficult to analyze. A brief overview of ethylene’s biosynthesis and signaling pathways and its different modulations are presented
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