Year of Publication

2007

Document Type

Dissertation

College

Agriculture

Department

Plant Physiology

First Advisor

Sharyn E. Perry

Abstract

AGAMOUS-Like 15 (AGL15) encodes a MADS-domain transcription factor that is preferentially expressed in the plant embryo, and may function as a regulator in embryonic developmental programs. A number of direct downstream targets of AGL15 have been identified, and while some of these target genes are induced in response to AGL15, others are repressed. Additionally, direct target genes have been analyzed that exhibit strong association with AGL15 in vivo, yet in vitro, AGL15 binds only weakly. Taken together these data suggest that AGL15 may form heterodimers, or ternary complexes with other proteins, thus modulating the specificity and function of AGL15 in planta. Yeast two-hybrid screens were undertaken to identify novel proteins able to interact with AGL15, and a number of interesting and potentially biologically important AGL15-interacting partners are reported here. These include members of a histone deacetylase complex, a COLD SHOCK DOMAIN (CSD)-containing protein, a Khomology domain/CCCH type zinc finger containing protein, a bZIP transcription factor, a homeobox-leucine zipper protein, a LATERAL ORGAN BOUNDARIES (LOB) domain containing protein, and an Agenet domain containing protein. Interactions between AGL15 and other MADS domain factors that are expressed in embryonic tissue, including SEPALLATA 3 (SEP3) have also been indentified. The regions of AGL15 that mediate interactions with the aforementioned proteins were mapped, and the capacity of these proteins to interact with other plant MADS-domain proteins tested. It is reported herein that AGL15 interacts with members of the SWI-INDEPENDENT 3/HISTONE DEACETYLASE (SIN3/HDAC) complex, and that AGL15 target genes are also responsive to an AGL15 interacting protein that is also a member of this complex, SIN3 ASSOCIATED POLYPEPTIDE OF 18 KD (SAP18). AGL15 can repress transcription in vivo, and a region essential to this repressive function contains an LxLxL motif that is conserved among putative orthologs of AGL15. What is more, the aforementioned motif mediates the association of AGL15 with SAP18 in yeast two-hybrid assays, thus providing a possible mechanism for explaining how role AGL15 regulates gene expression via recruitment of a histone deacetylase complex.

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