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


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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    • "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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    • "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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    • "MYC2, a positive regulator in JA signaling, was down-regulated. Chen [38] showed that MYC2 directly represses expression of PLT1 and PLT2 which are important transcription factors in auxin signaling pathways. Previous studies indicated that reduced levels of GA induced somatic embryo formation [39] and that LEC2 repressed the expression of GA biosynthesis gene GA3ox2 [14]. "
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