AGAMOUS-Like15 Promotes Somatic Embryogenesis in Arabidopsis and Soybean in Part by the Control of Ethylene Biosynthesis and Response      

Abstract

Many of the regulatory processes occurring during plant embryogenesis are still unknown. Relatively few cells are involved, and they are embedded within maternal tissues, making this developmental phase difficult to study. Somatic embryogenesis is a more accessible system, and many important regulatory genes appear to function similar to zygotic development, making somatic embryogenesis a valuable model for the study of zygotic processes. To better understand the role of the Arabidopsis (Arabidopsis thaliana) MADS factor AGAMOUS-Like15 (AGL15) in the promotion of somatic embryogenesis, direct target genes were identified by chromatin immunoprecipitation-tiling arrays and expression arrays. One potential directly up-regulated target was At5g61590, which encodes a member of the ethylene response factor subfamily B-3 of APETALA2/ETHYLENE RESPONSE FACTOR transcription factors and is related to Medicago truncatula SOMATIC EMBRYO-RELATED FACTOR1 (MtSERF1), which has been shown to be required for somatic embryogenesis in M. truncatula. Here, we report confirmation that At5g61590 is a directly expressed target of AGL15 and that At5g61590 is essential for AGL15's promotion of somatic embryogenesis. Because At5g61590 is a member of the ETHYLENE RESPONSE FACTOR family, effects of ethylene on somatic embryogenesis were investigated. Precursors to ethylene stimulate somatic embryogenesis, whereas inhibitors of ethylene synthesis or perception reduce somatic embryogenesis. To extend findings to a crop plant, we investigated the effects of ethylene on somatic embryogenesis in soybean (Glycine max). Furthermore, we found that a potential ortholog of AGL15 in soybean (GmAGL15) upregulates ethylene biosynthesis and response, including direct regulation of soybean orthologs of At5g61590/MtSERF1 named here GmSERF1 and GmSERF2, in concordance with the M. truncatula nomenclature.

The content of endogenous hormones and sugars in the process of early somatic embryogenesis in the tree fern Cyathea delgadii Sternb.

“…On the other hand, LEC2 activation induces YUC2 and YUC4 (YUCCA 2 and 4) genes involved in auxin biosynthesis (Stone et al 2008). The connection between auxin and genes that are specific for early SE, such as AGL15 (AGAMOUS-Like15) and FUS3 (FUSCA3) has also been documented (Stone et al 2008;Zheng et al 2013). It is commonly known that an appropriate level of auxin is required for SE induction (Ayil-Gutiérrez et al 2013;Gliwicka et al 2013).…”

Gene Regulation by the AGL15 Transcription Factor Reveals Hormone Interactions in Somatic Embryogenesis

“…To better understand how (Gm)AGL15 promotes SE, we assessed transcriptomes in response to (Gm)AGL15 accumulation in Arabidopsis and soybean (Zheng et al, 2009;Zheng and Perry, 2014). Comparison of the results in these two species led to the discovery that ethylene has a role in SE (Zheng et al, 2013) and that key embryo transcription factors are controlled directly by (Gm) AGL15 in both species (Zheng and Perry, 2014). Here, we report on (Gm)AGL15 regulation of auxin signaling and integration with GA metabolism.…”

“…Interestingly, a putative direct target of ARF6 that is activated by auxin treatment is the gene encoding another DELLA protein, GIBBER-ELLIC ACID INSENSITIVE (GAI), while ARF6 binds to regulatory regions of RGA, but a response was not demonstrated (Oh et al, 2014). Both (Gm)RGA and (Gm)GAI transcript accumulation show responses to 35S pro :GmAGL15, with apparent repression at 0 dac but significantly increased transcript at 3 dac on 2,4-D (Zheng et al, 2013). Thus, in a time frame in soybean from 0 to 3 dac on 2,4-D medium, when GmTIR1 is going from repressed to expressed in 35S pro : GmAGL15 compared with cv Jack and GmGA2ox6 is showing the opposite pattern (Fig.…”

Identification of LEC1, L1L and Polycomb Repressive Complex 2 genes and their expression during the induction phase of Medicago truncatula Gaertn. somatic embryogenesis

“…The 2,4-D artificial auxin, the popular SE inductor, is sufficient in many species to initiate a genetic program that leads to the establishment of cell lineages with an altered gene transcription pattern, and a different morphology and developmental fate (Gaspar et al 1996;Karami et al 2009). Different groups of genes are known to be expressed and essential during somatic embryogenesis, including WUSCHEL (WUS; Zuo et al 2002), AGAMOUS LIKE-15 (AGL15; Harding et al 2003;Zheng et al 2013), BABY-BOOM (BBM; Boutilier et al 2002) and LEAFY COTYLEDON (LECs, i.e. L1L, LEC1, LEC2, FUSCA3;Gaj et al 2005;Ledwoń and Gaj 2011).…”