Two transcription factors, MYB64 and MYB119, and their binding cis-regulatory element control egg cell-specific gene expression in Arabidopsis

With the growing emphasis on cell-type-specific gene expression in developmental regulation, genes exhibiting restricted expression patterns have emerged as critical regulators of plant reproductive processes. Notably, the egg cell-specific genes ECS1 (EGG CELL-SPECIFIC1) and EC1 (EGG CELL1) have been functionally characterized as key regulators required for successful fertilization. However, the mechanisms restricting these genes to a specific cell type remain largely unknown. In this study, we identified a cis-regulatory element, designated ESM (Egg cell-Specific Motif), that directs egg cell-specific expression of ECS1 in Arabidopsis thaliana. Two transcription factors, MYB64 and MYB119, were identified to bind to the ESM element. Loss of function of MYB64 and MYB119 resulted in pECS1::ECS1-GFP expression in both egg cells and synergid cells, leading to reduced LURE1.2 expression in synergid cells and defective pollen tube attraction. Furthermore, multiple known egg cell-specific genes were also regulated by MYB64/119-ESM module. Adding the ESM to the promoters of ES1 and ES2, two genes expressed in the female gametophyte, confined their expression specifically to the egg cell. Taken together, our findings reveal that a MYB64/119-ESM module contributes to the regulation of egg cell-specific gene expression.