Abstract
Main conclusion The ERF022 gene was found to affect embryogenic transition in somatic cells in Arabidopsis via the ethylene-related pathway. The study provides evidence that ERF022 - LEC2 interaction is involved in the auxin–ethylene crosstalk that operates in somatic embryogenesis induction. The ERF022 gene of the ERF family was previously identified among the transcription factor genes that were differentially expressed in an embryogenic culture of Arabidopsis. A strong inhibition of the gene was found to be associated with the induction of somatic embryogenesis (SE) and an erf022 mutant was indicated to display a substantially impaired capacity for SE. Therefore, the molecular function of ERF022 in the induction of SE was studied in the present work. A phenotype of an erf022 mutant was indicated as being related to an increased content of ethylene. The results further suggest that the ERF022 controls the genes that are involved in both the biosynthesis (ACS7) and signalling (ERF1, ETR1) of ethylene and indicate that the ERF022 is a new regulatory element in ethylene-related responses that negatively control the ethylene content and perception. It is proposed that the negative impact of ethylene on the induction of SE may result from a modulation of the auxin-related genes that control the embryogenic transition in somatic cells. Among them, the LEC2, which is a key regulator of the induction of SE through the stimulation of auxin synthesis, was possibly related to ERF022. The results of the study provide new hormone-related clues to define the genetic network that governs SE. A putative model of the regulatory pathway is proposed that is involved in the induction of SE in which the auxin–ethylene interactions are controlled by ERF022 and LEC2 and their targets.Electronic supplementary materialThe online version of this article (doi:10.1007/s00425-014-2225-9) contains supplementary material, which is available to authorized users.
Highlights
Somatic embryogenesis (SE), a plant regeneration process in which embryos are derived from the somatic tissue, is being studied intensively in order to reveal the molecular mechanisms of plant cell totipotency
To confirm that the inhibition of ERF022 is specific for the induction of somatic embryogenesis (SE), the gene expression level was tracked in Col-0 Immature zygotic embryos (IZEs) explants that had been cultured in vitro on different media in order to induce alternative morphogenic pathways including SE, shoot ORG and seedling development (Kraut et al 2011)
A significantly different from a highly embryogenic Col-0 culture level of ERF022 expression was indicated in cultures of the lec2, tan2-1 and cbp20 mutants that are significantly impaired in the SE response (Ledwonand Gaj 2009; Baster et al 2009) (Supplemental Fig. S1)
Summary
Somatic embryogenesis (SE), a plant regeneration process in which embryos are derived from the somatic tissue, is being studied intensively in order to reveal the molecular mechanisms of plant cell totipotency. Several genes encoding transcription factors (TFs) that have an essential function in the induction of SE have been identified in Arabidopsis, including BABY BOOM (BBM, Boutilier et al 2002), WUSCHEL (WUS, Zuo et al 2002), AGAMOUS-Like (AGL15, Harding et al 2003), LEAFY COTYLEDON (LEC, Gaj et al 2005), LEC1-LIKE (L1L, Yamamoto et al 2009), AtMYB115 and AtMYB118 (Wang et al 2009) and EMBRYOMAKER (EMK, Tsuwamoto et al 2010). Some AP2/ERF genes, including BBM (Boutilier et al 2002) and EMK (Tsuwamoto et al 2010) were indicated to promote embryo development in Arabidopsis somatic tissues, which implies that they have a specific function in the induction of SE
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