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

115 Molecular Genetic Analysis of Peroxisome Proliferation in Arabidopsis
Jianping Hu 1 , Travis Orth 1 , Sigrun Reumann 2 , Jilian Fan 1 , Sheng Quan 1 , Xinchun Zhang 1 , Mintu Desai 1 , Navneet
Kaur 1
1
MSU-DOE Plant Research Laboratory, Michigan State University, 2 Department of Plant Biochemistry,
University of Goettingen
Peroxisomes are highly dynamic organelles with diverse functions in eukaryotes. In addition to beta-oxidation
and H 2 O 2 degradation, which are shared by most eukaryotes, plant peroxisomes play central roles in a variety of plantspecific
processes, such as the glyoxylate cycle, photorespiration, nitrogen metabolism, hormone biosynthesis, and
plant responses to abiotic and biotic stresses. Peroxisomes change their size, shape and number in response to various
environmental stimuli to adapt to the new conditions. Although mechanisms controlling peroxisome abundance are
still elusive, a number of yeast proteins have been identified to be involved with peroxisome proliferation with mostly
unknown mechanisms. Plants lack obvious homologs to the majority of these yeast genes, suggesting that it is critical to
reveal the plant-specific aspects of this fundamental cell biological process. As a starting point to identify components of
the plant peroxisome proliferation machinery, we characterized the five-member Arabidopsis PEX11 protein family. We
have shown that the PEX11 genes were amplified independently in the plant lineage after the split of different kingdoms,
and that Arabidopsis and rice each contain two PEX11 subgroups. Using GFP-fusions and subcellular fractionations, we
demonstrated the peroxisomal localization of all five PEX11 proteins and showed PEX11c and PEX11d to be integral
membrane proteins. Overexpression studies suggested that different subfamilies of the Arabidopsis PEX11 family may
play divergent roles during peroxisome proliferation. Consistent with this view, only a subset of AtPEX11 proteins was
able to complement the yeast pex11 null mutant. Arabidopsis mutants created by virus-induced gene silencing and RNA
interference are being analyzed. In addition, we performed genetic and biochemical screens to identify new peroxisome
division/proliferation mutants and nuclear proteins that control the expression of key peroxisome proliferation genes.
Mutants showing abnormal peroxisomal size or shape and a putative transcriptional factor that binds to the promoter
of a light-inducible PEX11 gene have been isolated. Our research will help to establish a mechanistic model of plant
peroxisome division and proliferation, which is currently lacking.
116 A Gain-of-Function Mutation in the Pleiotropic Drug Resistance Transporter AtPDR9
Confers Resistance to the Herbicide 2,4-D
Hironori Ito, William Gray
University of Minnesota
Arabidopsis contains 15 genes encoding members of the pleiotropic drug resistance (PDR) family of ABC transporters.
These proteins have been speculated to be involved in the detoxification of xenobiotics, however little experimental
support of this hypothesis has been obtained to date. Here we report our characterization of the Arabidopsis AtPDR9
gene. We isolated a semi-dominant, gain-of-function mutant, designated atpdr9-1, that exhibits increased tolerance to the
auxinic herbicide 2,4-D. Reciprocally, loss-of-function mutations in AtPDR9 confer 2,4-D hypersensitivity. This altered
auxin sensitivity defect of atpdr9 mutants is specific for 2,4-D and closely related compounds as these mutants respond
normally to the endogenous auxins IAA and IBA. We demonstrate that 2,4-D, but not IAA, transport is affected by
mutations in atpdr9 suggesting that the AtPDR9 transporter specifically effluxes 2,4-D out of plant cells without affecting
endogenous auxin transport. The semi-dominant atpdr9-1 mutation affects an extremely highly conserved domain present
in all known plant PDR transporters. The single amino acid change results in increased AtPDR9 abundance and provides
a novel approach for elucidating the function of plant PDR proteins.