75 Integrating Membrane Transport with Male Gametophyte ... - TAIR

149 Mechanisms of Interaction and Consequences of Protein Complexes Involving AGAMOUS-
Like 15 (AGL15), a MADS-Domain Transcription Factor that Preferentially Accumulates in
the Plant Embryo
Kristine Hill 1 , Huai Wang 2 , Sharyn Perry 1
1
University of Kentucky , 2 University of Wisconsin
AGAMOUS-Like 15 (AGL15) encodes a MADS-box transcription factor that is preferentially expressed in the plant
embryo, and is believed to be an important regulator in embryonic developmental programs. Research in our lab has
identified a number of downstream targets of AGL15, and while some of these target genes are induced in response to
AGL15, others are repressed. A number of direct target genes have been analyzed that exhibit strong responses to AGL15
levels in vivo, yet in vitro, AGL15 binds only weakly. Taken together these data suggested that AGL15 may form heterodimers,
or ternary complexes with other proteins, thus modulating AGL15’s specificity and function in planta. The Yeast
Two-Hybrid system has been used to address this question and putative interactors of AGL15 have been identified. The
mechanisms of interactions and the consequences of these associations in planta will be presented.
A motif within the C-terminal domain of AGL15, which is conserved in putative orthologs of AGL15, appears to
function as a repression domain in vivo. One protein, identified in the Yeast Ttwo-Hybrid screen as a potential interacting
protein of AGL15, is a member of the SIN3 histone deacetylase complex (HDAC), and preliminary data suggests that
the aforementioned motif might mediate AGL15’s association with, and recruitment of, members of this complex.
Co-Immunoprecipitation and Chromatin Immunoprecipitation (ChIP) approaches are being employed to study the
biological functionality of protein-protein interactions involving AGL15 in planta, and to ultimately elucidate the subset
of downstream targets regulated by AGL15 in conjunction with the different protein partners identified.
150 Characterisation of fn10, A Novel Germination Mutant In Arabidopsis thaliana
Tara Holman 1, 2 , Steven Footitt 2 , Freddie Theodoulou 2 , Michael Holdsworth 1
1
University of Nottingham, Sutton Bonington Campus, Loughborough, Leics. LE12 5RD, UK, 2 Rothamsted
Research, Harpenden, Herts. AL5 2JQ, UK
The regulation of germination is controlled by many genetic loci. A large number of these loci are involved in the
biosynthesis and signalling of two phytohormones - abscisic acid (ABA) and gibberellins (GA). These two hormones
have an antagonistic relationship: ABA promotes dormancy, GA promotes germination.
Seed dormancy is an evolutionary strategy that delays the germination of a proportion of the seed set until successive
seasons. It also prevents the seed from germinating whilst attached to the mother plant.
Here we describe the positional cloning and the phenotypic characterisation of fn10, a novel germination mutant in
Arabidopsis thaliana. This mutant was identified from a forward genetic screen for mutants with a reduction in germination
potential. Also identified in this screen was the cts-1 (comatose-1) mutant (Russell et al., 2000; Footitt et al., 2002).
Studies of the germination characteristics of fn10 have shown that it requires a prolonged period to after-ripen, it is
hypersensitive to ABA for germination, and seedlings fail to establish on sucrose. The germination potential of fn10 can
be increased with either exogenous GA or a period of stratification.
Double mutants have been constructed between fn10 and abi1-1 (ABA insensitive-1), aba1-1 (ABA deficient-1), and
rgl2 (RGA-like-1) (Koornneef et al., 1982; Koornneef et al., 1984; Lee et al., 2002). The abi1-1 mutant is insensitive
to ABA, the aba1-1 is disrupted in ABA biosynthesis and the rgl2 mutant displays constitutive GA signalling effects.
Phenotypic analysis of the double mutants has shown that ABI1 is epistatic to FN10, and FN10 is epistatic to both ABA1
and RGL2.
A model for the action of FN10 in the regulation of germination is proposed.
Reference List
Footitt,S. et al. Embo Journal (2002) 21, 2912-2922.
Koornneef,M. et al. Theoretical and Applied Genetics (1982) 61, 385-393.
Koornneef,M. et al. Physiologia Plantarum (1984) 61, 377-383.
Lee,S.C. et al. Genes & Development (2002) 16, 646-658.
Russell,L. et al. Development (2000) 127, 3759-3767.