A Transcription Factor γMYB1 Binds to the P1BS cis-Element and Activates PLA2-γ Expression with its Co-Activator γMYB2.

Phospholipase A2(PLA2) hydrolyzes phospholipid molecules to produce two products that are both precursors of second messengers of signaling pathways and signaling molecules per se.Arabidopsis thaliana PLA2paralogs (-β,-γand-δ) play critical roles during pollen development, pollen germination and tube growth. In this study, analysis of thePLA2-γpromoter using a deletion series revealed that the promoter region -153 to -1 is crucial for its pollen specificity. Using a yeast one-hybrid screening assay with thePLA2-γpromoter and an Arabidopsis transcription factor (TF)-only library, we isolated two novel MYB-like TFs belonging to the MYB-CC family, denoted here as γMYB1 and γMYB2. By electrophoretic mobility shift assay, we found that these two TFs bind directly to the P1BS (phosphate starvation response 1-binding sequence)cis-element of thePLA2-γpromoter. γMYB1 alone functioned as a transcriptional activator forPLA2-γexpression, whereas γMYB2 directly interacted with γMYB1 and enhanced its activation. Overexpression ofγMYB1in the mature pollen grain led to increased expression of not only thePLA2-γgene but also of several genes whose promoters contain the P1BScis-element and which are involved in the Pi starvation response, phospholipid biosynthesis and sugar synthesis. Based on these results, we suggest that the TF γMYB1 binds to the P1BScis-element, activates the expression ofPLA2-γwith the assistance of its co-activator, γMYB2, and regulates the expression of several target genes involved in many plant metabolic reactions.