Phosphatidylinositol 5-phosphate links dehydration stress to the activity of ARABIDOPSIS TRITHORAX-LIKE factor ATX1.
BACKGROUND
Changes in gene expression enable organisms to respond to environmental stress. Levels of cellular lipid second messengers, such as the phosphoinositide PtdIns5P, change in response to a variety of stresses and can modulate the localization, conformation and activity of a number of intracellular proteins. The plant trithorax factor (ATX1) tri-methylates the lysine 4 residue of histone H3 (H3K4me3) at gene coding sequences, which positively correlates with gene transcription. Microarray analysis has identified a target gene (WRKY70) that is regulated by both ATX1 and by the exogenous addition of PtdIns5P in Arabidopsis. Interestingly, ATX1 contains a PtdIns5P interaction domain (PHD finger) and thus, phosphoinositide signaling, may link environmental stress to changes in gene transcription.


RESULTS
Using the plant Arabidopsis as a model system, we demonstrate a link between PtdIns5P and the activity of the chromatin modifier ATX1 in response to dehydration stress. We show for the first time that dehydration leads to an increase in cellular PtdIns5P in Arabidopsis. The Arabidopsis homolog of myotubularin (AtMTM1) is capable of generating PtdIns5P and here, we show that AtMTM1 is essential for the induced increase in PtdIns5P upon dehydration. Furthermore, we demonstrate that the ATX1-dependent gene, WRKY70, is downregulated during dehydration and that lowered transcript levels are accompanied by a drastic reduction in H3K4me3 of its nucleosomes. We follow changes in WRKY70 nucleosomal K4 methylation as a model to study ATX1 activity at chromatin during dehydration stress. We found that during dehydration stress, the physical presence of ATX1 at the WRKY70 locus was diminished and that ATX1 depletion resulted from it being retained in the cytoplasm when PtdIns5P was elevated. The PHD of ATX1 and catalytically active AtMTM1 are required for the cytoplasmic localization of ATX1.


CONCLUSIONS
The novelty of the manuscript is in the discovery of a mechanistic link between a chromatin modifying activity (ATX1) and a lipid (PtdIns5P) synthesis in a signaling pathway that ultimately results in altered expression of ATX1 dependent genes downregulated in response to dehydration stress.
School of Biological Sciences, University of Nebraska at Lincoln, Lincoln, Nebraska, United States of America.
Ivan
I
Ndamukong
David R
DR
Jones
Hanna
H
Lapko
Nullin
N
Divecha
Zoya
Z
Avramova
D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000378:metabolism*; D001483:Base Sequence; D047369:Chromatin Immunoprecipitation; D002851:Chromatography, High Pressure Liquid; D002855:Chromatography, Thin Layer; D017931:DNA Primers; D011495:Histone-Lysine N-Methyltransferase; D009994:Osmolar Concentration; D018129:Phosphatidylinositol Phosphates / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013312:Stress, Physiological; D013347:Subcellular Fractions / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism*; D014867:Water
D029681:Arabidopsis Proteins; D017931:DNA Primers; D018129:Phosphatidylinositol Phosphates; D014157:Transcription Factors; C113567:phosphatidylinositol 5-phosphate; D014867:Water; C504056:At2g31650 protein, Arabidopsis; D011495:Histone-Lysine N-Methyltransferase