Characterization of MADS domain genes expressed during embryogenesis in Arabidopsis thaliana

MADS domain genes play important developmental roles as transcriptional regulators. One goal of my research was to define the developmental role of AGL15, a MADS domain gene preferentially expressed in embryos. I also explored the possibility that other MADS domain genes function during the embryonic phase.; To understand how AGL15 is regulated at the protein level, I studied the accumulation of epitope-tagged forms of AGL 15 in Arabidopsis . Previous work indicated that AGL15 becomes nuclear-localized during embryo development and that nuclear localization is accompanied by a change in molecular weight of the AGL15 protein (Perry et al., 1999. Plant Physiol. 120:121--129). However, my work shows that only one predominant form of AGL15 accumulates during embryo development in Arabidopsis, and that this protein is associated with the nucleus.; To understand AGL15's role in plant development, I screened for an agl15 loss of function allele and characterized the effect of loss of AGL15 on plant development. Plants homozygous for a null agl15 allele show no developmental defects. Functional redundancy among closely related members of the MADS domain gene family is common; therefore, I explored the possibility that AGL18, the family member most closely related to AGL15, acts redundantly with AGL15 during plant development. Studies of AGL15-GUS and AGL18-GUS translational fusion proteins indicated that the expression patterns of AGL15 and AGL18 overlap in several tissues including the embryo and endosperm. Also, Arabidopsis plants ectopically expressing AGL18 exhibit defects in floral organ abscission and senescence similar to plants that ectopically express AGL15. This suggests that AGL15 and AGL18 share regulatory roles in plant development.; To uncover the full extent of possible genetic redundancy in the control of embryo development by MADS domain proteins, I used RT-PCR to identify MADS domain genes that are expressed during the embryonic phase. Gene specific primers were designed to 50 MADS domain genes, and 32 of these genes were expressed in embryonic tissue. Therefore, I concluded that there is potential for a great deal of redundancy in the regulation of embryonic programs by MADS domain genes.