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) up-regulates 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.
Highlights
The inaccessibility of higher plant embryos during early development has made it difficult to study this stage of the life cycle
We performed expression microarray analysis to determine transcriptome changes in response to increased (35Spro: AGL15) and decreased AGL15 accumulation in a shoot apical meristem somatic embryo (SAM somatic embryogenesis (SE)) system (Zheng et al, 2009)
Prior work found that the percentage of seedlings with SAM SE development was positively correlated with AGL15 accumulation (Harding et al, 2003; Thakare et al, 2008)
Summary
The inaccessibility of higher plant embryos during early development has made it difficult to study this stage of the life cycle. AGAMOUS-Like (AGL15) and FUSCA3 (FUS3) do not cause SE to form on seedlings when ectopically expressed but do lead to the proliferation of embryogenic tissue (35Spro:AGL15) or embryo features in seedlings (ML1pro:FUS3). Both of these genes have been found to be up-regulated in response to auxin (Gazzarrini et al, 2004; Zhu and Perry, 2005). To understand how AGL15 promotes SE, direct and indirect regulated genes were identified (Wang et al, 2004; Zhu and Perry, 2005; Zheng et al, 2009). A number of genes related to ethylene biosynthesis and response were identified as regulated by GmAGL15, including potential MtSERF1 orthologs (referred to as GmSERF1 and GmSERF2). Results are presented to identify the connection between (Gm)AGL15 and At5g61590/ GmSERF1/GmSERF2 and to better understand the function of At5g61590 and hormone interaction in SE in Arabidopsis and soybean
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