STRAWBERRY FRUIT PROTEIN WITH A NOVEL INDOLE-ACYL POST-TRANSLATIONAL MODIFICATION

Fruit of the diploid strawberry, Fragaria vesca L. 'Yellow Wonder' contain indole-3-acetic acid (IAA) covalently attached to specific strawberry proteins. Protein-conjugated IAA accounts for between 0.4 and 4 ng of IAA per gram fresh weight of tissue in achenes, and in receptacle tissue. Immunoblotting using a specific antibody to IAA-glycine linked to BSA detected IAA proteins in both achenes and receptacles. This antibody detected a single band in receptacle tissue and multiple bands in achenes. Proteins in a broad, immunoreactive, spot from 2D PAGE analysis were previously subjected to in-gel trypsin digestion followed by analysis with LC-MS/MS. Peptide fragment analysis tentatively identified this protein as either a chaperonin related to the hsp60 class of proteins or, alternatively, an ATP-synthase. PAGE of proteins from a developmental series of fruit of the commercially grown octoploid strawberry (F. × ananassa L. 'Ovation') showed that the IAA-protein is more abundant early in fruit development than in mature unripe berries. The same developmental pattern was observed in fruit from the octoploid progenitor species F. virginiana L. 'LH50-4', however, the opposite pattern, low in early development but increasing with maturity, was observed in the other octoploid progenitor, F. chiloensis 'Scott's Creek'. Immunological analysis of tissue prints indicated that IAA-proteins are present throughout the cortex and achenes in very young fruit, but are localized in epidermal tissue and achenes in more mature unripe fruit. This IAA modified protein in fruit tissue is the first such protein described with predicted functions related to stress responses and the first IAA protein described in developing and actively growing plant tissues.