Molecular and genetic analysis of the MADS-box Type I transcription factors AGAMOUS-LIKE 28 and AGAMOUS-LIKE 36

Abstract

Abstract

Seed development requires a coordinated interplay between different transcriptional programs in the embryo, the endosperm and the maternally derived seed coat. In angiosperms, the embryo and the endosperm are products of the double fertilization of the egg cell and the central cell by two pollen sperm cells. A highly specialized type of transcriptional regulation in the fertilization products is imprinting, an epigenetic phenomenon that leads to parent-of-origin dependent expression of specific genes. The number of imprinted genes identified in plants has until recently been very low compared to mammals and several genome-wide approaches has been initiated in order to identify novel imprinted genes. In a microarray screen, a cluster of AGAMOUS-LIKE (AGL) Type I MADS-box encoding genes were de-regulated in endosperm that lacked the paternal genome in the endosperm. Within this cluster, AGL36 was shown to be imprinted, and only expressed from the maternal genome. AGL36 imprinting is controlled by the activity of METHYLTRANSFERASE1 (MET1) maintenance DNA methyltransferase and DEMETER (DME) DNA glycosylase. In addition the active maternal allele of AGL36 is regulated throughout endosperm development by components of the FIS Polycomb Repressive Complex 2 (PRC2).

In this thesis we wanted to further study the regulation and biological role of AGL36 and other related genes identified in the Type I MADS-box cluster. Using an AGL36 reporter transgene with imprinted expression, we show that the proximal promoter region of AGL36 is not sufficient to reverse imprinting in a mutant MET1 background. AGL36 has previously been shown to interact with AGL28, and here we show that AGL28 is a novel imprinted gene, that is only expressed from the maternal genome, and demonstrate that AGL28 imprinting may not depend on the action of MET1.