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Published on March 10, 2006; 10.1104/pp.106.078592

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Received February 2, 2006
Returned for revision February 22, 2006
Accepted March 2, 2006

Rice HPLs with Unique Expression Patterns Generate Distinct Aldehyde Signatures in Arabidopsis

E. W. Chehab , G. Raman , J.W. Walley , J.V. Perea , G. Banu , S. Theg , and K. Dehesh *

Section of Plant Biology, University of California-Davis, Davis, CA, 95616

* Corresponding author; email: kdehesh{at}ucdavis.edu.

HYDROPEROXIDE LYASE (HPL) genes encode enzymes that catalyze the cleavage of fatty acid hydroperoxides into aldehydes and oxoacids. There are three HPLs in rice designated OsHPL1 through OsHPL3. To explore the possibility of differential functional activities among these genes, we have examined their expression patterns and biochemical properties of their encoded products. Transcript analysis indicates that these genes have distinct patterns and levels of expression. OsHPL1 is ubiquitously expressed, OsHPL2 is expressed in the leaves and leaf sheaths, whereas OsHPL3 is wound-inducible and expressed exclusively in leaves. OsHPLs also differ in their substrate preference as determined by in vitro enzyme assays using 9/13-hydroperoxy linolenic (HPOT) and linoleic (HPOD) acids as substrates. OsHPL1 and OsHPL2 metabolize 9/13-hydroperoxides, whereas OsHPL3 metabolizes 13-HPOT exclusively. Sequence alignments of the HPL enzymes have identified signature residues potentially responsible for the substrate specificity/preference of these enzymes. All three OsHPLs are chloroplast-localized as determined by chloroplast import assays and GFP fusion studies. Aldehyde measurements in transgenic Arabidopsis plants overexpressing individual OsHPL-GFP fusions indicate that all rice HPLs are functional in a heterologous system, and each of them generates a distinct signature of the metabolites. Interestingly, these aldehydes were only detectable in leaves, but not in roots, despite similar levels of OsHPL-GFP proteins in both tissues. Similarly, there were undetectable levels of aldehydes in rice roots, in spite of the presence of OsHPL1 transcripts. Together, these data suggest that additional tissue-specific mechanism(s), beyond transcript and HPL enzyme abundance, regulate the levels of HPL-derived metabolites.




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