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

199 The Trichome Pock Phenotype of agb1 and pom1
Zachary Larson-Rabin, Christopher Day
University of Wisconsin-Madison
Socket cells, which are specialized epidermal cells surrounding the base of Arabidopsis trichomes, differentiate
following an unknown recruitment mechanism. These cells, numbering twelve on average in wild-type Columbia, serve
to support the trichome. We have identified two mutants characterized by trichome pocks, which are deep indentations
of the leaf surface at the base of some trichomes. The pocks correlate with an increase in socket cell number.
We have mapped one mutant and found that it has a loss-of-function mutation in AGB1, the beta subunit of the
heterotrimeric G-protein complex. Some of the pleiotropic phenotypes of the agb1 mutant have been described before,
and include auxin and ABA hypersensitivity, erecta-like aerial defects, and root morphology and growth alterations. In
this poster, we will describe the undocumented trichome pock phenotype of agb1.
Another mutant that exhibits the trichome pock phenotype is the erh2 allele of POM-POM1 (POM1/ERH2/ELP1/
AtCTL1). Trichomes of the erh2 allele show extra socket cells, sometimes as many as 30 per trichome. These plants also
have root morphology phenotypes similar to agb1. In addition, stomata often form between socket cells or even adjacent
to trichomes. This is not seen in wild-type or in agb1, in which stomata always form outside the socket cell zone. The
gene product of POM1, a chitinase-like protein, has been implicated in repressing ethylene production and signaling.
Our poster will describe our characterization of the trichome pock phenomenon, with regard to possible intercellular
signals that control socket cell number.
200 Adenosine Kinase Deficient Lines Display Abnormal Development
Sarah Schoor 1 , Katja Engel 1 , Filomena Ng 1 , Sanghyun Lee 1 , Neil Emery 2 , Barb Moffatt 1
1
Univeristy of Waterloo, Waterloo Ontario, Canada, 2 Trent Univeristy, Peterborough Ontario, Canada
By recycling adenosine into AMP, adenosine kinase (ADK; EC 2.7.1.20) plays a key role in maintaining nucleotide
pools and methylation. In Arabidopsis, ADK is represented by two highly similar isoforms, ADK1 (At3g09820) and ADK2
(At5g03300). Aside from establishing that ADK1 is expressed at higher levels than ADK2 throughout Arabidopsis, no
distinct role has been assigned to either isoform. In order to establish the roles of these isoforms, as well as ADK activity
itself, gene silencing lines (sADK) and T-DNA mutants lacking either ADK1 or ADK2 were identified. The metabolism
and development of these mutants were then examined by establishing their remaining ADK activity and documenting
their corresponding growth rate, leaf and meristem development and DNA methylation using HPLC analysis. The results
indicate no unique role for either ADK1 or ADK2, since the removal of either isoform results in decreased ADK activity
but no discernable phenotypic changes. However, reducing overall levels of ADK activity resulted in severe changes
to plant development, with lower ADK activity causing more severe phenotypes. Some of the abnormalities associated
with the silencing include: decreased DNA methylation, smaller roots, wrinkled leaves, enlarged inflorescent meristems,
clustered inflorescences, delayed leaf and silique senescence and reduced stem development. Secondary shoots that
eventually develop on sADK plants are morphologically similar to those of wild-type Arabidopsis (i.e. contain cauline
leaves and non-clustered inflorescences). We are using ADK-deficient lines generated by overexpression of ADK-GFP
fusion proteins to compare silencing in secondary vs primary shoots. In addition, transformation with a constitutively
expressed adenosine deaminase cDNA alleviates the abnormal phenotype of the sADK lines and suggests that increased
adenosine is leading to these traits.