2018 ASHS Annual Conference

Strawberry fruit growth is a classic system for studying auxin signaling between tissues during fruit development. The juicy flesh of the strawberry results from enlargement of the stem tip (the receptacle) underlying the carpels in response to auxin and gibberellin produced by the developing achenes, the botanical true fruit. The auxin originates in the achenes, which spiral up the outside of the receptacle. In later stages of berry development, auxin slows the ripening process. The literature describes a pattern of free auxin (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. Auxin is found in plants primarily

conjugated to various amino acids and sugars. Strawberry tissues are capable of synthesizing auxin

conjugates, and transcriptome data shows the expression of genes involved in IAA conjugate formation and

hydrolysis throughout embryo development and subsequent seedling growth. Using a highly sensitive, high

resolution, liquid chromatography-mass spectrometric method, we have now identified all the low molecular

weight indole-auxin amino acid conjugates in achenes of F. vesca as consisting only of IAA-aspartate and

IAA-glutamate. In contrast to what is believed to occur in Arabidopsis, we determined that IAA-aspartate and

IAA-glutamate are hydrolyzed by seedlings to provide a source of free IAA for growth.