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

297 Rapid and economic mapping of regulatory loci in complex traits using gene expression
profiling
Remco Van Poecke, Masanao Sato, Lisa Lenarz-Wyatt, Fumiaki Katagiri
University of Minnesota
Genetic variation is a useful tool to dissect complex traits, such as inducible defense against pathogens in plants.
An excellent source of genetic variation can be found in naturally occurring populations. However, use of such natural
variation is hampered by the quantitative nature of complex traits. Thus, dissection of complex traits using natural
variation commonly involved tedious genetic crossing schemes and genotypic analyses, such as creation, phenotyping,
and genotyping of recombinant inbred lines. We are currently developing a rapid and economical method to detect and
map regulatory loci involved in complex traits. The concept of this method is to finely dissect the phenotype for a complex
trait using expression profiles and to identify parts of phenotype (i.e., expression of some genes) that segregate in a
Mendelian manner and that are controlled in trans. We initiated characterization of Arabidopsis accessions in response
to infection of an avirulent bacterial strain by conventional phenotyping and expression profiling. To reduce the cost of
expression profiling, we are using a dedicated small-scale DNA microarray. We will report that the dedicated microarray
is an excellent tool to study natural variation in Arabidopsis and that results of the phenotypic and expression profile
characterization of the parental accessions are well correlated.
This project was supported by the National Research Initiative of the USDA Cooperative State Research, Education
and Extension Service, grant number 2004-35301-14525.
298 Arabidopsis Bax-Inhibitor 1 Functions As An Attenuator Of Biotic And Abiotic Types of Cell
Death
Naohide Watanabe, Eric Lam
Biotech Center, Rutgers The State University of New Jersey
Programmed cell death (PCD) is a common process in eukaryotes during development and in response to pathogens
and stress signals. Bax inihibitor-1 (BI-1) is a small protein of 25-27 kDa with 6 or 7 predicted transmembrane domains
and is mainly localized in the membrane of the endoplasmic reticulum (ER). BI-1 is proposed to be a cell death suppressor
that is conserved in both animals and plants, but the physiological importance of BI-1 and the impact of its loss of function
in plants are still unclear. In this study, we identified and characterized two independent Arabidopsis mutants with a
T-DNA insertion in the AtBI1 gene. The phenotype of atbi1-1 and atbi1-2, with a C-terminal missense mutation and a
gene knockout, respectively, was indistinguishable from wild-type plants under normal growth conditions. However,
these two mutants exhibit accelerated progression of cell death upon infiltration of leaf tissues with a PCD-inducing
fungal toxin fumonisin B1 (FB1) and increased sensitivity to heat shock-induced cell death. Under these conditions,
expression of AtBI1 mRNA was up-regulated in wild-type leaves prior to the activation of cell death, suggesting that
increase of AtBI1 expression is important for basal suppression of cell death progression. Overexpression of AtBI1 in the
two homozygous mutant backgrounds rescued the accelerated cell death phenotypes. In addition, we found that AtBI1
expression is enhanced under the ER stress conditions, suggesting that AtBI1 could modulate ER stress-induced cell
death. Together, our results provide direct genetic evidence for a role of BI-1 as an attenuator for cell death progression
triggered by both biotic and abiotic types of cell death signals in Arabidopsis.
N. Watanabe & E. Lam (2006) Arabidopsis Bax Inhibitor-1 functions as an attenuator of biotic and abiotic types of cell death. Plant Journal
45(6):884-894.