Dataset Information

Auxin acts as a local morphogenetic trigger to specify lateral root founder cells.

ABSTRACT: Plants exhibit an exceptional adaptability to different environmental conditions. To a large extent, this adaptability depends on their ability to initiate and form new organs throughout their entire postembryonic life. Plant shoot and root systems unceasingly branch and form axillary shoots or lateral roots, respectively. The first event in the formation of a new organ is specification of founder cells. Several plant hormones, prominent among them auxin, have been implicated in the acquisition of founder cell identity by differentiated cells, but the mechanisms underlying this process are largely elusive. Here, we show that auxin and its local accumulation in root pericycle cells is a necessary and sufficient signal to respecify these cells into lateral root founder cells. Analysis of the alf4-1 mutant suggests that specification of founder cells and the subsequent activation of cell division leading to primordium formation represent two genetically separable events. Time-lapse experiments show that the activation of an auxin response is the earliest detectable event in founder cell specification. Accordingly, local activation of auxin response correlates absolutely with the acquisition of founder cell identity and precedes the actual formation of a lateral root primordium through patterned cell division. Local production and subsequent accumulation of auxin in single pericycle cells induced by Cre-Lox-based activation of auxin synthesis converts them into founder cells. Thus, auxin is the local instructive signal that is sufficient for acquisition of founder cell identity and can be considered a morphogenetic trigger in postembryonic plant organogenesis.

SUBMITTER: Dubrovsky JG

PROVIDER: S-EPMC2438385 | biostudies-literature | 2008 Jun

REPOSITORIES: biostudies-literature

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Auxin acts as a local morphogenetic trigger to specify lateral root founder cells.

Dubrovsky Joseph G JG Sauer Michael M Napsucialy-Mendivil Selene S Ivanchenko Maria G MG Friml Jirí J Shishkova Svetlana S Celenza John J Benková Eva E

Proceedings of the National Academy of Sciences of the United States of America 20080616 25

Plants exhibit an exceptional adaptability to different environmental conditions. To a large extent, this adaptability depends on their ability to initiate and form new organs throughout their entire postembryonic life. Plant shoot and root systems unceasingly branch and form axillary shoots or lateral roots, respectively. The first event in the formation of a new organ is specification of founder cells. Several plant hormones, prominent among them auxin, have been implicated in the acquisition ...[more]

PMID: 18559858

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Project description:Protein phosphorylation is instrumental to early signaling events. Studying system-wide phosphorylation in relation to processes under investigation requires a quantitative proteomics approach. In Arabidopsis, auxin application can induce pericycle cell divisions and lateral root formation. Initiation of lateral root formation requires transcriptional reprogramming following auxin-mediated degradation of transcriptional repressors. The immediate early signaling events prior this derepression are virtually uncharacterized. To identify the signal molecules responding to auxin application we used the Lateral Root Inducible System which was previously developed to trigger synchronous division of pericycle cells. To identify and quantify the early signaling events following this induction we combined 15N based metabolic labeling and phospho-enrichment and applied a mass spectrometry based approach. In total, 3068 phosphopeptides were identified from auxin treated root tissue. This experiment represents one of the largest quantitative phosphoprotein dataset on Arabidopsis to date. Key proteins responding to auxin treatment included the MDR and PIN2 auxin carriers, auxin response factor2, suppressor of auxin resistance3 and sorting nexin1 (SNX1). Mutational analysis of Serine16 of SNX1 showed that overexpression of the mutated forms of SNX1led to retarded growth and reduction of lateral root formation due to the reduced outgrowth of the primodium, showing proof of principle for our approach. Data Processing: All MS/MS spectra were centroided and merged to a single peak list file using MaxQuant (version 1.0.13.13), which was searched using the Mascot search engine (version 2.2.0, Matrix Science) containing a total 67344 entries (which includes contaminants and an equivalent number of decoy sequences) generated from the publicly available Arabidopsis database (The Arabidopsis Information Resource (TAIR9); June 2009; file name, TAIR9_pep_20090619) with carbamidomethylcysteine as a fixed modification. Oxidized methionine and phosphorylation (serine, threonine, and tyrosine) were searched as variable modifications. Searches were done with tryptic specificity allowing two miscleavages and an initial tolerance on mass measurement of 50 ppm in MS mode and 0.6 Da for MS/MS ions and score cutoff of 20. The resulting .dat files were exported and filtered for a <1% false discovery rate (FDR) at the peptide level using in-house developed software Rockerbox (Version1.1.0) (35). Relative quantification ratios of the identified phosphopeptides and protein were derived by MSQuant (MSQ2.0b4, 2010-02-25) (36). Proteins were quantified with at least two unique non phosphopeptides or single peptide with a score no less than 60. The phospho peptide ratio was normalized by dividing the ratio of its protein of origin. To determine whether phosphorylation ratios for normalized peptides were significantly different a p-value was generated using significance B which is part of the MaxQuant package. The changes were considered significant at a p-value of 0.05 or less. For comparison at the phosphopeptide level the most recent the full dataset with experimental sites was downloaded from PhosPhAt 4.0. Phosphopeptides with ambiguous residues denoted as (s), (t), etc., were converted to S and T, respectively. In addition we used Supplementary Table S1 from Lan et al., (2012) for phosphopeptide comparison. Modifications other than nonambiguous phosphorylation were ignored resulting in a reduction from the original 879 phosphopeptides to 556 peptides. We used pep2pro 'TAIR10 wos' dataset for comparison at the protein level.

Dataset Information

Auxin acts as a local morphogenetic trigger to specify lateral root founder cells.

Publications

Auxin acts as a local morphogenetic trigger to specify lateral root founder cells.

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