| Description |
Coenocytic development is a hallmark of angiosperm reproductive development, occurring in both female gametophyte and nuclear endosperm development. In both developmental processes a cell undergoes multiple rounds of nuclear divisions without cytokinesis to generate a single multinucleate cell, also called a coenocyte. The coenocyte then undergoes a cellularization and differentiation process in which cell walls partition the coenocyte into a multicellular structure consisting of the final differentiated tissue. The molecular mechanisms that regulate coenocytic development during female gametogenesis and nuclear endosperm development are poorly understood. Here I use genetic and gene expression techniques to characterize the function of two transcription factors, MYB64 and MYB119. I show that MYB64 and MYB119 are required to promote cellularization and differentiation during coenocytic development within the female gametophyte. Female gametophytes that inherit mutations in both MYB64 and MYB119 fail to cellularize and differentiate, resulting in enlarged coenocytic gametophytes containing supernumerary nuclei. Additionally I show that MYB119 expression is regulated by the histidine-kinase CKI1, which implicates CKI1-dependent two-component signaling in gamete formation. I also investigate the regulation of nuclear endosperm development by analyzing mutations affecting AGL62, which is required to promote coenocytic endosperm development and inhibits endosperm cellularization. Mutations affecting AGL62 result in precocious endosperm cellularization and early seed lethality. I use microarray analysis to identify genes misregulated in agl62 seeds, and show that many of the misregulated genes are normally expressed much later in seed development. I provide evidence that the seed maturation and ZHOUPI transcriptional pathways are precociously activated in agl62 seeds, suggesting the agl62 phenotype is heterochronic in nature. I also identify a group of four transcription factors closely related to MYB64 and MYB119 as being misregulated in agl62 seeds. I further investigate whether this group of endosperm-expressed transcription factors function in a similar manner to promote cellularization and differentiation within the coenocytic endosperm. Together my data define transcriptional networks involved in the regulation of coenocytic development in both female gametophyte and nuclear endosperm development. |
