The Arabidopsis DREB2 genetic pathway is constitutively repressed by basal phosphoinositide-dependent phospholipase C coupled to diacylglycerol kinase

Abstract

Phosphoinositide-dependent phospholipases C (PI-PLCs) are activated in response to various stimuli. They utilize substrates provided by type III-Phosphatidylinositol-4 kinases (PI4KIII) to produce inositol triphosphate and diacylglycerol (DAG) that is phosphorylated into phosphatidic acid (PA) by DAG-kinases (DGKs). The roles of PI4KIIIs, PI-PLCs, and DGKs in basal signaling are poorly understood. We investigated the control of gene expression by basal PI-PLC pathway in Arabidopsis thaliana suspension cells. A transcriptome-wide analysis allowed the identification of genes whose expression was altered by edelfosine, 30 μM wortmannin, or R59022, inhibitors of PI-PLCs, PI4KIIIs, and DGKs, respectively. We found that a gene responsive to one of these molecules is more likely to be similarly regulated by the other two inhibitors. The common action of these agents is to inhibit PA formation, showing that basal PI-PLCs act, in part, on gene expression through their coupling to DGKs. Amongst the genes up-regulated in presence of the inhibitors, were some DREB2 genes, in suspension cells and in seedlings. The DREB2 genes encode transcription factors with major roles in responses to environmental stresses, including dehydration. They bind to C-repeat motifs, known as Drought-Responsive Elements that are indeed enriched in the promoters of genes up-regulated by PI-PLC pathway inhibitors. PA can also be produced by phospholipases D (PLDs). We show that the DREB2 genes that are up-regulated by PI-PLC inhibitors are positively or negatively regulated, or indifferent, to PLD basal activity. Our data show that the DREB2 genetic pathway is constitutively repressed in resting conditions and that DGK coupled to PI-PLC is active in this process, in suspension cells and seedlings. We discuss how this basal negative regulation of DREB2 genes is compatible with their stress-triggered positive regulation.

Importance of phosphoinositide-dependent signaling pathways in the control of gene expression in resting cells and in response to phytohormones

“…5 Transcriptomic studies of Arabidopsis cells in suspension using CATMA microarray chips, 6 allowed us to establish a list of genes that showed an altered expression for each inhibitor. [7][8][9] Comparing the lists showed an over representation of genes for which wortmannin and edelfosine (or wortmannin and U73122) had the same effect. 9 The common effect of inhibiting PI4K and inhibiting PI-PLC is to decrease the total amount of products generated by PI-PLC (Fig.…”

The Arabidopsispi4kIIIβ1β2double mutant is salicylic acid-overaccumulating: a new example of salicylic acid influence on plant stature

“…3,4 In the Arabidopsis thaliana genome, 4 type III-PI4K genes can be found, clustered into 2 a and 2 b subtypes. The AtPI4KIIIa2 is more likely a pseudogene.…”

The phosphoinositide dependent-phospholipase C pathway differentially controls the basal expression ofDREB1andDREB2genes

“…DREB2D expression is not stimulated by the inhibitors of these enzymes, while DREB2F and DREB2G transcripts could never be detected in any of the conditions tested. 7 …”

“…6 The PI-PLC/DGK pathway is active in nonstimulated Arabidopsis cells or plants. 7,8 We recently showed that this basal activity negatively regulated the expression of DREB2A, DREB2B, DREB2C, DREB2E, and DREB2H genes. Indeed, when inhibiting the activity of PI-PLC by edelfosine or U73122, or when inhibiting the activity of DGK by R59022 or R59949, the expression of these genes was upregulated in Arabidopsis suspension cells.…”

“…Indeed, when inhibiting the activity of PI-PLC by edelfosine or U73122, or when inhibiting the activity of DGK by R59022 or R59949, the expression of these genes was upregulated in Arabidopsis suspension cells. 7 We wanted to know if this was also the case for the DREB1 genes. Cells were treated by U73122 or its inactive analog U73343.…”