A transcription factor γMYB1 binds to the P1BS cis-element and activates PLA2-γ expression with its co-activator γMYB2

Abstract

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 PLA2 paralogs (-β, -γ and -δ) play critical roles during pollen development, pollen germination and tube growth. In this study, analysis of the PLA2-γ 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 PLA2-γ 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 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 the PLA2-γ promoter. γMYB1 alone functioned as a transcriptional activator for PLA2-γ expression, whereas γMYB2 directly interacted with γMYB1 and enhanced its activation. Overexpression of γMYB1 in the mature pollen grain led to increased expression of not only the PLA2-γ 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 γMYB1 binds to the P1BS cis-element, activates the expression of PLA2-γ with the assistance of its co-activator, γMYB2, and regulates the expression of several target genes involved in many plant metabolic reactions.