Indole-3-acetylaspartate and indole-3-acetylglutamate, the IAA-amide conjugates in the diploid strawberry achene, are hydrolyzed in growing seedlings
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Indole-3-acetylaspartate and indole-3-acetylglutamate are the stored auxin amino acid conjugates of the achene of the diploid strawberry and serve as sources of auxin during seedling growth.
The edible part of the strawberry, a pseudocarp, has long been known to enlarge in response to auxin produced by the developing achenes, the botanical true fruit. Auxin homeostasis involves a complex interaction between biosynthesis, conjugate formation and hydrolysis, catabolism and transport. Strawberry tissues are capable of synthesizing auxin conjugates, and transcriptome data support the expression of genes involved in IAA conjugate formation and hydrolysis throughout embryo development and subsequent seedling growth. Using a highly sensitive and selective mass spectrometric method, we identified all the low molecular weight indole-auxin amino acid conjugates in achenes of F. vesca as consisting of indole-3-acetylaspartate (IAasp) and indole-3-acetylglutamate (IAglu). In contrast to what has been proposed to occur in Arabidopsis, we determined that IAasp and IAglu are hydrolyzed by seedlings to provide a source of free IAA for growth.
KeywordsAuxin conjugates Conjugate hydrolysis IAA amidohydrolase Indole-3-acetic acid Seed auxin precursors Strawberry achenes Woodland strawberry
Liquid chromatography–tandem mass spectrometry
This work was supported by USDA/ARS CRIS 8042-21220-254-00D, by Agriculture and Food Research Initiative competitive awards no. 2018-67011-28056 and 2018-67013-27503 from the USDA National Institute of Food and Agriculture, by the NSF Plant Genome Research Program grant IOS-1238812 as well as support from the Minnesota Agricultural Experiment Station and by the Gordon and Margaret Bailey Endowment for Environmental Horticulture. We thank Paul Fiesel for the synthesis of the [13C6]IAglu used in this study, Dr. Adrian Hegeman for help with figure graphics, and Dr. Laura Shannon for advice on the evolutionary analysis of the IAA amino acid conjugate hydrolases.
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