Indole-3-acetyl-aspartate and indole-3-acetyl-glutamate, the IAA-amide conjugates in the diploid strawberry achene, are hydrolyzed in growing seedlings

Authors: TANG, QIAN - University Of Minnesota; YU, PENG - University Of Minnesota; TILLMAN, MOLLY - University Of Minnesota; COHEN, JERRY - University Of Minnesota; Slovin, Janet

Submitted to: Planta
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/24/2018
Publication Date: 12/8/2018
Citation: Tang, Q., Yu, P., Tillman, M., Cohen, J., Slovin, J.P. 2018. Indole-3-acetyl-aspartate and indole-3-acetyl-glutamate, the IAA-amide conjugates in the diploid strawberry achene, are hydrolyzed in growing seedlings. Planta. 249(4):1073-1085. https://doi.org/10.1007/s00425-018-3061-0.
DOI: https://doi.org/10.1007/s00425-018-3061-0

Interpretive Summary: Strawberries are an economically important fruit crop in the U.S., generating $2.8 billion in 2014 and are well-loved because of their delicious flavor and attractive color. While it has been known for over 50 years that the hormone auxin is responsible for the growth of the fruit, only recently has molecular biology pointed to how the plant might be providing the auxin for this growth of the fruit and of the plant. Modern, sensitive machines allowed us to analyze what forms of auxins are packed into the seeds by the mother plant for growth of the seedling. We identified two such forms, and experimentally showed that these forms are the source of the hormone for growing seedlings. This is the first time that these particular forms have been shown to be used for growth rather than being forms the plant discards. This work will enhance scientist’s understanding of the hormones and genes involved in production of improved fruit and plant varieties.

Technical Abstract: 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. The classical literature describes a pattern of free auxin (indole-3-acetic acid; IAA) accumulation in the developing berry suggestive of active metabolic and/or transport activity that sustains the enlargement of the receptacle after embryo development is complete. In diploid strawberry, Fragaria vesca, embryo development is complete at 10 to 13 days after pollination, yet fruit expansion continues well past that point. 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-acetylgutamate (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.