A novel transcription factor required for synergid cells in Arabidopsis

The female gametophyte plays a critical role in essentially every step of the reproductive process. During pollen tube growth, the female gametophyte participates in directing the pollen tube to the ovule. Upon fertilization, female gametophyte-expressed genes control the initiation of seed development. During seed development, female gametophyte-expressed gene products play a role in controlling embryo and endosperm development. In spite of its important role in plant reproduction, very little is known on a molecular or genetic level about female gametophyte development or reproductive function. To understand the gene regulatory network in the female gametophyte, the forward genetics approach has been taken for over a decade. However, the approach is not sufficient to understand the whole network. Therefore, I started a reverse genetics approach and established the ms1-di1 screening. From an RT-PCR screen of the MYB family, I identified 24 genes most likely expressed in the female gametophyte. One of the genes was MY898. MYB98 is a member of the R2R3-MYB gene family, the members of which likely encode transcription factors. In the context of the ovule, MYB98 is expressed exclusively in the synergid cells, and mutations in this gene affect the female gametophyte specifically. myb98 female gametophytes are affected in two unique features of the synergid cell, pollen tube guidance and the filiform apparatus. These data suggest that MYB98 controls the development of specific features within the synergid cell during female gametophyte development. To study the synergid cell gene regulatory network, MYB98 is the best candidate because MYB98 is the only known transcription factor functioning in the synergid cells. To identify the upstream regulator of the MYB98, I started the promoter deletion analysis and I identified several putative cis regulatory elements. These elements most likely bind to several transcription factors and facilitate the gene regulatory network in the synergid cells.