engleski

The Role of MATH/BTB Proteins of Wheat and Maize in Asymmetric Divisions during Megagametogenesis and Early Embryogenesis

By screening egg cell and proembryo cDNAs libraries of wheat and maize we have identified four differentially expressed genes encoding proteins with both a MATH and a BTB domain, designated as TaMAB1-3 and ZmMAB1 (MATH and BTB), respectively. Only one such gene has been functionally characterized in C. elegans (Mel26) as a key regulator required for the first asymmetric zygote division. While one of the four plant MABs is expressed constitutively during vegetative growth (TaMAB3), TaMAB1 and ZmMAB1 display an egg cell/early embryo-specific expression pattern. Moreover, TaMAB2 expression was detected exclusively after fertilisation. Tracking a TaMAB2-GFP fusion during cell division revealed that the protein is present at the nuclear envelope and the preprophase band. In transgenic Arabidopsis plants, egg cell derived TaMAB2-GFP is always inherited to the basal cell of the 2-celled proembryo, and thereafter localized in micropylar located suspensors cell. This asymmetric inheritance of TaMAB2-GFP was also observed in transient expression studies of dividing suspension cells. Interaction studies have shown that TaMAB2 may assemble as a homodimer but also interacts with AtCUL3, indicating the involvement of TaMAB2 in ubiquitin mediated proteosomal degradation. Downregulation of ZmMAB1 leads to an arrest of female gametophyte development. In summary the specific expression pattern.as well as asymmetric and cell-cycle modulated protein localisation suggest a role of MABs as intrinsic polarity factors during female gamete and early embryo formation, and perhaps asymmetric cell divisions in general. Current work is focused on the identification of downstream MAB substrates.

MATH-BTB; megagametogehesis; embryogenesis; ubiquitin

nije evidentirano