Plant Cell Advance Online Publication
Published on December 28, 2006; 10.1105/tpc.106.046227
Received July 25, 2006
Returned for revision November 8, 2006
Accepted December 1, 2006
Reduction of Benzenoid Synthesis in Petunia Flowers Reveals Multiple Pathways to Benzoic Acid and Enhancement in Auxin Transport
Irina Orlova 1, Amy Marshall-Colón 1, Jennifer Schnepp 1, Barbara Wood 1, Marina Varbanova 2, Eyal Fridman 2, Joshua J. Blakeslee 1, Wendy Ann Peer 1, Angus S. Murphy 1, David Rhodes 1, Eran Pichersky 2, and Natalia Dudareva 1*
1 Department of Horticulture and Landscape Architecture, Purdue University, West Lafayette, Indiana 47907
2 Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, Michigan 48109
* To whom correspondence should be addressed. E-mail: dudareva{at}purdue.edu.
In plants, benzoic acid (BA) is believed to be synthesized from Phe through shortening of the propyl side chain by two carbons. It is hypothesized that this chain shortening occurs via either a  -oxidative or non--oxidative pathway. Previous in vivo isotope labeling and metabolic flux analysis of the benzenoid network in petunia (Petunia hybrida) flowers revealed that both pathways yield benzenoid compounds and that benzylbenzoate is an intermediate between L-Phe and BA. To test this hypothesis, we generated transgenic petunia plants in which the expression of BPBT, the gene encoding the enzyme that uses benzoyl-CoA and benzyl alcohol to make benzylbenzoate, was reduced or eliminated. Elimination of benzylbenzoate formation decreased the endogenous pool of BA and methylbenzoate emission but increased emission of benzyl alcohol and benzylaldehyde, confirming the contribution of benzylbenzoate to BA formation. Labeling experiments with 2H5-Phe revealed a dilution of isotopic abundance in most measured compounds in the dark, suggesting an alternative pathway from a precursor other than Phe, possibly phenylpyruvate. Suppression of BPBT activity also affected the overall morphology of petunia plants, resulting in larger flowers and leaves, thicker stems, and longer internodes, which was consistent with the increased auxin transport in transgenic plants. This suggests that BPBT is involved in metabolic processes in vegetative tissues as well.
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