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The MADS box transcription factor Arabidopsis (Arabidopsis thaliana) AGAMOUS-LIKE15 (AGL15) and a putative ortholog from soybean (Glycine max), GmAGL15, are able to promote somatic embryogenesis (SE) in these plants when ectopically expressed. SE is an important means of plant regeneration, but many plants, or even particular cultivars, are recalcitrant for this process. Understanding how (Gm)AGL15 promotes SE by identifying and characterizing direct and indirect downstream regulated genes can provide means to improve regeneration by SE for crop improvement and to perform molecular tests of genes. Conserved transcription factors and the genes they regulate in common between species may provide the most promising avenue to identify targets for SE improvement. We show that (Gm)AGL15 negatively regulates auxin signaling in both Arabidopsis and soybean at many levels of the pathway, including the repression of AUXIN RESPONSE FACTOR6 (ARF6) and ARF8 and TRANSPORT INHIBITOR RESPONSE1 as well as the indirect control of components via direct expression of a microRNA-encoding gene. We demonstrate interaction between auxin and gibberellic acid in the promotion of SE and document an inverse correlation between bioactive gibberellic acid and SE in soybean, a difficult crop to transform. Finally, we relate hormone accumulation to transcript accumulation of important soybean embryo regulatory factors such as ABSCISIC ACID INSENSITIVE3 and FUSCA3 and provide a working model of hormone and transcription factor interaction in the control of SE. [ABSTRACT FROM AUTHOR]

Multiple factors, including the MADS-domain proteins AGAMOUS-LIKE15 (AGL15) and AGL18, contribute to the regulation of the transition from vegetative to reproductive growth. AGL15 and AGL18 were previously shown to act redundantly as floral repressors and upstream of FLOWERING LOCUS T (FT) in Arabidopsis (Arabidopsis thaliana). A series of genetic and molecular experiments, primarily focused on AGL15, was performed to more clearly define their role. agl15 agl18 mutations fail to suppress ft mutations but show additive interactions with short vegetative phase (svp) mutations in ft and suppressor of constans1 (soc1) backgrounds. Chromatin immunoprecipitation analyses with AGL15-specific antibodies indicate that AGL15 binds directly to the FT locus at sites that partially overlap those bound by SVP and FLOWERING LOCUS C. In addition, expression of AGL15 in the phloem effectively restores wild-type flowering times in agl15 agl18 mutants. When agl15 agl18 mutations are combined with agl24 svp mutations, the plants show upward curling of rosette and cauline leaves, in addition to early flowering. The change in leaf morphology is associated with elevated levels of FT and ectopic expression of SEPALLATA3 (SEP3), leading to ectopic expression of floral genes. Leaf curling is suppressed by sep3 and ft mutations and enhanced by soc1 mutations. Thus, AGL15 and AGL18, along with SVP and AGL24, are necessary to block initiation of floral programs in vegetative organs. [ABSTRACT FROM AUTHOR]

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 traction 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/ETHYL 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. [ABSTRACT FROM AUTHOR]

AGAMOUS-Like15 (AGL15) is a MADS domain transcriptional regulator that promotes somatic embryogenesis by binding DNA and regulating gene expression. Chromatin immunoprecipitation (CHIP) analysis previously identified DNA fragments with which AGL15 associates in vivo, and a low-throughput approach revealed a role for AGL15 in gibberellic acid catabolism that is relevant to embryogenesis. However, higher throughput methods are needed to identify targets of AGL15. Here, we mapped AGL15 in vivo binding sites using a ChIP-chip approach and the Affymetrix tiling arrays for Arabidopsis thaliana and found that ∼2000 sites represented in three biological replicates of the experiment are annotated to nearby genes. These results were combined with high-throughput measurement of gene expression in response to AGL15 accumulation to discriminate responsive direct targets from those further downstream in the network. LEAFY COTYLEDON2, FUSCA3, and ABA INSENSITIVE3, which encode B3 domain transcription factors that are key regulators of embryogenesis, were identified and verified as direct target genes of AGL15. Genes identified as targets of the B3 genes are also targets of AGL15, and we found that INDOLEACETIC ACID-INDUCED PROTEIN30 is involved in promotion of somatic embryo development. The data presented here and elsewhere suggest that much cross-regulation occurs in gene regulatory networks underpinning embryogenesis. [ABSTRACT FROM AUTHOR]

In this paper, using Swan's graph theoretic method on directed path approach to Amitsur-Levitzki theorem, we obtain a new class of polynomial identities on the ring of n x n matrices over any commutative ring with 1. Standard and Chang-Giambruno-Sehgal polynomial identities are the special examples of our conclusions. [ABSTRACT FROM AUTHOR]