A Transcription Factor gamma MYB1 Binds to the P1BS cis-Element and Activates PLA(2)-gamma Expression with its Co-Activator gamma MYB2

Abstract

Phospholipase A(2) (PLA(2)) hydrolyzes phospholipid molecules to produce two products that are both precursors of second messengers of signaling pathways and signaling molecules per se. Arabidopsis thaliana PLA(2) paralogs (-beta, -gamma and -delta) play critical roles during pollen development, pollen germination and tube growth. In this study, analysis of the PLA(2)-gamma promoter 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 the PLA(2)-gamma promoter and an Arabidopsis transcription factor (TF)-only library, we isolated two novel MYB-like TFs belonging to the MYB-CC family, denoted here as gamma MYB1 and gamma MYB2. 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 the PLA(2)-gamma promoter. gamma MYB1 alone functioned as a transcriptional activator for PLA(2)-gamma expression, whereas gamma MYB2 directly interacted with gamma MYB1 and enhanced its activation. Overexpression of gamma MYB1 in the mature pollen grain led to increased expression of not only the PLA(2)-gamma gene but also of several genes whose promoters contain the P1BS cis-element and which are involved in the Pi starvation response, phospholipid biosynthesis and sugar synthesis. Based on these results, we suggest that the TF gamma MYB1 binds to the P1BS cis-element, activates the expression of PLA(2)-gamma with the assistance of its co-activator, gamma MYB2, and regulates the expression of several target genes involved in many plant metabolic reactions.