Poster: Organelle Biogenesis

Abs # 1147: Characterization of a Lon homolog in Arabidopsis peroxisomes

Presenter:	Olsen, Laura J., ljo@umich.edu
Authors	Olsen, Laura J. (A)   Johnson, Tanya L. (A)
Affiliations:	(A): University of Michigan

Protein degradation in plants is a complex process involving multiple proteolytic pathways. The presence of proteolytic activity has been reported in several cellular compartments, including vacuoles, chloroplasts, mitochondria, and the Golgi apparatus., Little is known, however, about the proteases localized to peroxisomes. We report here the cloning and characterization of a Lon protease homolog (AtLon2) localized to plant peroxisomes. AtLon2 has significant amino acid similarity to the E.coli Lon protease, its homolog in yeast, and identified sequences localized to the mitochondria in Arabidopsis and maize. A well-conserved ATP binding domain and a catalytic domain with the requisite serine residue also suggest this AtLon2 has conserved protease function. Interestingly, the last three predicted amino acids encode a consensus type 1 peroxisomal targeting signal. To test the hypothesis that this Lon homolog is targeted to peroxisomes, in vitro import assays and subcellular fractionations were performed. To our knowledge this is the first known Lon protease located in peroxisomes. In vitro transcribed and translated AtLon2 was also incubated with resorufin-labeled casein to characterize its protease activity. In yeast, the mitochondrial Lon homolog has been shown to be essential to respiratory function, and its loss results in a petite phenotype (Suzuki et al. 1994). We screened the ABRC T-DNA insertion library and obtained a line that is homozygous for an insertion in the last exon of the AtLon2 gene. This insertion removes the peroxisomal targeting signal from the extreme carboxyl terminus of the protein. Phenotypic analysis of the mutant plant and RT-PCR expression data will also be presented.