Article

The Basic Helix-Loop-Helix Transcription Factor MYC2 Directly Represses PLETHORA Expression during Jasmonate-Mediated Modulation of the Root Stem Cell Niche in Arabidopsis

State Key Laboratory of Plant Genomics, National Centre for Plant Gene Research, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China.
The Plant Cell (Impact Factor: 9.34). 09/2011; 23(9):3335-52. DOI: 10.1105/tpc.111.089870
Source: PubMed

ABSTRACT

The root stem cell niche, which in the Arabidopsis thaliana root meristem is an area of four mitotically inactive quiescent cells (QCs) and the surrounding mitotically active stem cells, is critical for root development and growth. We report here that during jasmonate-induced inhibition of primary root growth, jasmonate reduces root meristem activity and leads to irregular QC division and columella stem cell differentiation. Consistently, jasmonate reduces the expression levels of the AP2-domain transcription factors PLETHORA1 (PLT1) and PLT2, which form a developmentally instructive protein gradient and mediate auxin-induced regulation of stem cell niche maintenance. Not surprisingly, the effects of jasmonate on root stem cell niche maintenance and PLT expression require the functioning of MYC2/JASMONATE INSENSITIVE1, a basic helix-loop-helix transcription factor that involves versatile aspects of jasmonate-regulated gene expression. Gel shift and chromatin immunoprecipitation experiments reveal that MYC2 directly binds the promoters of PLT1 and PLT2 and represses their expression. We propose that MYC2-mediated repression of PLT expression integrates jasmonate action into the auxin pathway in regulating root meristem activity and stem cell niche maintenance. This study illustrates a molecular framework for jasmonate-induced inhibition of root growth through interaction with the growth regulator auxin.

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    • "However, the strong correlation among root length, meristem size and protoxylem element position observed in pea roots might cease under stress conditions, interfering with cell division, elongation or maturation events[3]. Of note, the stress signaling hormone jasmonic acid (JA) interferes with the auxin pathway involved in the maintenance of the root zonation by repressing PLT expression[9]. Furthermore, reactive oxygen species have also been involved in meristem size specification by controlling the transition between cell proliferation and differentiation, independently from the cytokinin/auxin pathway[10]. "

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    • "In general, the regulatory effect of JA through auxin on LR formation is the net result of two competing mechanisms: JA promotes the ANTHRANILATE SYNTHASE ALPHA SUBUNIT 1 (ASA1)-dependent auxin synthesis and JA reduces PIN-dependent auxin transport (Sun et al. 2009). JA is also integrated into auxin-mediated root meristem activity via MYC2/JASMONATE INSENSITIVE1 (MYC2)-dependent repression of PLETHORA (PLT) expression (Chen et al. 2011). Another report, however, suggested that an auxin independent mechanism of the JA regulation of root development exists (Raya-González et al. 2012). "
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    ABSTRACT: Phytohormone jasmonates (JA) play essential roles in plants, such as regulating development and growth, responding to environmental changes, and resisting abiotic and biotic stresses. During signaling, JA interacts, either synergistically or antagonistically, with other hormones, such as salicylic acid (SA), gibberellin (GA), ethylene (ET), auxin, brassinosteroid (BR), and abscisic acid (ABA), to regulate gene expression in regulatory networks, conferring physiological and metabolic adjustments in plants. As an important staple crop, rice is a major nutritional source for human beings and feeds one third of the world's population. Recent years have seen significant progress in the understanding of the JA pathway in rice. In this review, we summarize the diverse functions of JA, and discuss the JA interplay with other hormones, as well as light, in this economically important crop. We believe that a better understanding of the JA pathway will lead to practical biotechnological applications in rice breeding and cultivation.
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    • "This group includes the TIFY domain genes JAZ1 (AT1G19180), JAZ2 (AT1G74950), JAZ5 (AT1G17380), JAZ6 (AT1G72450), JAZ7 (AT2G34600), JAZ8 (AT1G30135), JAZ9 (AT1G70700), JAS1/JAZ10 (AT5G13220), two WRKY genes involved in pathogen response, WRKY18 (AT4G31800) and WRKY40 (AT1G80840) [50], the bHLH-family AIB (AT2G46510) [51] and MYC2 (AT1G32640) [52] and the AP2/ERF RRTF1 (AT4G34410). Interestingly, chromatin immunoprecipitation experiments have shown that WRKY40 binds JAZ8 and RRTF1 regulatory regions [53], while MYC2 was recently shown to be involved in jasmonate-dependent root development inhibition [54]. "
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    ABSTRACT: Uncovering the complex transcriptional regulatory networks (TRNs) that underlie plant and animal development remains a challenge. However, a vast amount of data from public microarray experiments is available, which can be subject to inference algorithms in order to recover reliable TRN architectures. In this study we present a simple bioinformatics methodology that uses public, carefully curated microarray data and the mutual information algorithm ARACNe in order to obtain a database of transcriptional interactions. We used data from Arabidopsis thaliana root samples to show that the transcriptional regulatory networks derived from this database successfully recover previously identified root transcriptional modules and to propose new transcription factors for the SHORT ROOT/SCARECROW and PLETHORA pathways. We further show that these networks are a powerful tool to integrate and analyze high-throughput expression data, as exemplified by our analysis of a SHORT ROOT induction time-course microarray dataset, and are a reliable source for the prediction of novel root gene functions. In particular, we used our database to predict novel genes involved in root secondary cell-wall synthesis and identified the MADS-box TF XAL1/AGL12 as an unexpected participant in this process. This study demonstrates that network inference using carefully curated microarray data yields reliable TRN architectures. In contrast to previous efforts to obtain root TRNs, that have focused on particular functional modules or tissues, our root transcriptional interactions provide an overview of the transcriptional pathways present in Arabidopsis thaliana roots and will likely yield a plethora of novel hypotheses to be tested experimentally.
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