WOX2 and STIMPY-LIKE/WOX8 promote cotyledon boundary formation in Arabidopsis

Molecular and Computational Biology, University of Southern California, Los Angeles, CA 90089, USA.
The Plant Journal (Impact Factor: 5.97). 07/2012; 72(4). DOI: 10.1111/j.1365-313X.2012.05113.x
Source: PubMed


One of the key events in dicot plant embryogenesis is the emergence of the two cotyledon primordia, which marks the transition from radial symmetry to bilateral symmetry. In Arabidopsis thaliana, the three CUP-SHAPED COTYLEDON (CUC) genes are responsible for determining the boundary region between the cotyledons. However, the mechanisms controlling their transcription activation are not well understood. Previous studies found that several WOX family homeobox transcription factors are involved in embryo apical patterning and cotyledon development. Here we show that WOX2 and STIMPY-LIKE (STPL/WOX8) act redundantly to differentially regulate the expression of the CUC genes in promoting the establishment of the cotyledon boundary, without affecting the primary shoot meristem. Loss of both WOX2 and STPL results in reduced CUC2 and CUC3 expression in one side of the embryo, but an expansion of the CUC1 domain. Furthermore, we found that STPL is expressed in the embryo proper, and its activation is enhanced by the removal of WOX2, providing an explanation for the functional redundancy between WOX2 and STPL. Additional evidence also showed that WOX2 and STPL function independently in regulating different aspects of local auxin gradient formation during early embryogenesis.

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Available from: Xuelin wu, Oct 13, 2014
    • "WOX2, in turn, would activate the CUC1 gene, which does not contain the trimethylation mark or the Sph/RY motif. Both CUC1 and WOX2 are TFs involved in the formation of an apical–basal axis, and cotyledons in the embryo (Ikeda et al., 2006; Kwon et al., 2006; Breuninger et al., 2008; Ueda et al., 2011; Lie et al., 2012), and their expression is needed during early embryogenesis. WOX2 transcript levels decreased during early embryo maturation, as VAL1 transcript levels increased and remained completely repressed during middle maturation when VAL1 was present . "
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    ABSTRACT: Developing Arabidopsis seeds accumulate oils and seed storage proteins synthesized by the pathways of primary metabolism. Seed development and metabolism are positively regulated by transcription factors belonging to the LAFL (LEC1, AB13, FUSCA3 and LEC2) regulatory network. The VAL gene family encodes repressors of the seed maturation program in germinating seeds, although they are also expressed during seed maturation. The possible regulatory role of VAL1 in seed development has not been studied to date. Reverse genetics revealed that val1 mutant seeds accumulated elevated levels of proteins compared to the wild type, suggesting that VAL1 functions as a repressor of seed metabolism. However, metabolomes and the levels of ABA, auxin, and jasmonate derivatives did not change significantly in developing embryos in the absence of VAL1. Two VAL1 splice variants were identified through RNA sequencing analysis: a full-length and a truncated form lacking the plant-homeodomain-like domain associated with epigenetic repression. None of the transcripts encoding the core LAFL network transcription factors were affected in val1 embryos. Instead, activation of VAL1 by FUSCA3 appears to result in repression of a subset of seed maturation genes downstream of core LAFL regulators as 39% of transcripts in the FUSCA3 regulon were de-repressed in the val1 mutant. The LEC1 and LEC2 regulons also responded but to a lesser extent. Additional 832 transcripts that were not LAFL targets were de-repressed in val1 mutant embryos. These transcripts are candidate targets of VAL1, acting through epigenetic and/or transcriptional repression. This article is protected by copyright. All rights reserved.
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    • "⁎ Corresponding author. and cotyledon boundary formation (Breuninger et al., 2008; Haecker et al., 2004; Lie et al., 2012; Wu et al., 2007). In Arabidopsis and tomato, accumulation of WOX4 mRNA is found in the developing vascular bundle of root and shoot lateral organs, which promotes differentiation and/ or maintains the vascular procambium (Ji et al., 2010). "
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    ABSTRACT: The WUSCHEL-related homeobox (WOX) genes are important transcription regulators participated in plant development processes. Rice genome encodes (Oryza sativa L. spp. indica) at least 13 WOX members. In this study, a systematic microarray-based gene expression profiling of eleven WOX genes was performed for the whole life cycle of rice at 16 different tissues/organs of MH63 (rice indica cultivar), which included eight reproductive organs and eight vegetative tissues. The results demonstrated that four genes (OsWUS, OsNS1/OsNS2, OsWOX3 and OsWOX9A) were specifically expressed in panicle and endosperm development, and six genes (OsWOX5, OsWOX9B, OsWOX9D, OsWOX11, OsWOX12A and OsWOX12B) were preferentially expressed in seeds (72h after imbibitions) during root emergence or growth. In situ hybridization analysis revealed differential transcript levels of OsWOX4, OsWOX5, OsWOX9A and OsWOX12B during panicle development and embryogenesis. Results of qRT-PCR showed that expression of four rice WOX genes (OsWOX5, OsWOX11, OsWOX12B and OsWOX12A) was up- or down-regulated by plant hormones (auxin, cytokinin and gibberellin). More interestingly, most WOX genes were responsive to abiotic stress stimuli of drought, salt and cold. The molecular studies presented here will further provide insight in understanding the functions of rice WOX gene family in rice development, hormone signaling, and abiotic stress response.
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    ABSTRACT: During embryogenesis, the basic body plan of an organism develops from a unicellular zygote. In most flowering plants, the polar zygote divides asymmetrically, making visible the apical-basal axis in the early embryo. The molecular mechanisms governing how the zygote polarizes and how this polarity is linked to embryo axis formation have been obscure, mainly owing to the difficulties to access the zygote that is deeply embedded in the maternal tissue. In this review, we summarize recent findings identifying key regulators in Arabidopsis and developing novel approaches in various plant species, which altogether set the stage for unraveling embryo axis formation.
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