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

363 Progress Towards the Cloning of sw4.1., the Major Gene for Natural Seed Size Variation in
Tomato: From Fine Mapping to BAC Sequence Analysis
Cintia Orsi, Steven Tanksley
Cornell University
Seed size is a life-history trait whose significance is emphasized by its ecological, agronomic and evolutionary
importance. In nature, seed size is associated with fitness, playing a major role in seed size-number trade-off. Seed size
increase was also one of the consequences of the domestication process for most of the crops, including seed crops.
Despite the obvious importance of seed size, the genetic and molecular bases for variation in seed size in nature is still
largely unknown. Previous studies in tomato have identified a QTL, sw4.1., which accounts for a large portion of the
seed size difference between wild and cultivated tomatoes. Nearly isogenic lines have been created for the fine mapping
of this seed size QTL. A subsequent screening of 10,000 F2 individuals from a cross between the NILs has allowed us to
narrow down the seed-size controlling region to 30 kb within a single BAC clone. A combination of association genetics
and transformation/complementation experiments are being used to pinpoint the specific gene involved and the nature
of the genetic changes in this gene (or its promoter) which are causally related to natural variation in seed size.
*Supported by grants from USDA-NRI, NSF and Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq)/Brazil.
364 Using small molecules to probe natural variation: characterization of strain-specific
xenobiotic metabolism in Arabidopsis
Rachel Puckrin, Sean Cutler
University of Toronto
Plants are exposed to a diverse array of xenobiotics (natural and manmade chemicals) that can affect their growth,
development and productivity. Additionally, plants frequently metabolize xenobiotics into new forms that are toxic
to humans and / or have adverse environmental effects. In spite of its importance, many aspects of plant xenobiotic
metabolism are poorly understood at the biochemical level. We are tackling this problem using a genetic approach that
aims to define genes involved in xenobiotic uptake, metabolism and excretion in Arabidopsis which we are defining as
XEN loci (for xenobiotic disposition loci). To identify XEN loci we have used HPLC coupled to Diode Array Detection
(HPLC-DAD) to survey the uptake, metabolism and excretion of ~400 structurally diverse xenobiotics on the Col , Ler
and Cvi ecotypes. The compounds selected for analysis by HPLC included approximately 280 compounds identified in
a chemical genetic screen as inhibitors of hypocotyl cell expansion and an additional 120 randomly selected compounds
that are not active in hypocotyl cell expansion assays. Greater than 85% percent of the compounds analysed are detectable
by HPLC-DAD in extracts prepared from drug treated seedlings; of these, ~35% of show evidence of metabolism and
~18% show evidence of excretion. Comparison of HPLC-DAD profiles across the ecotypes surveyed reveals that multiple
compounds show strain-specific differences in metabolism; recombinant inbred lines are currently being used to dissect the
genetic basis of these differences. Our results suggest that small molecules are effective probes of metabolic differences
between ecotypes and thus can be used to expand the toolkit used for dissecting natural variation in Arabidopsis.