An Auxin-Conjugated Strawberry Fruit Protein

Authors: COHEN, JERRY - U.MINN.; PARK, SEIJIN - U. MINN.; Slovin, Janet

Submitted to: North American Strawberry Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 7/25/2007
Publication Date: 3/11/2008
Citation: Cohen, J.D., Park, S., Slovin, J.P. 2008. An Auxin-Conjugated Strawberry Fruit Protein. North American Strawberry Conference Proceedings. Page 108.

Interpretive Summary: High summertime temperatures reduce the amount and quality of strawberry fruit that growers are able to produce. The reason for this is not understood. We examined the proteins that are normally made by strawberry fruit and found that one of these proteins unexpectedly has a plant hormone attached. It has been known for a long time that the hormone is produced by developing strawberry “seeds”, and causes the fruit to grow. It also affects ripening. We previously showed that the protein appears to be involved in resistance to heat stress. We have determined that this protein accumulates early in development of commercially grown fruit types, and that it goes away as the fruit matures. The same pattern of accumulation occurs in one parent species of commercial strawberry, but the opposite was found for the other parent species. We also show that this protein was located in different regions of the fruit during fruit growth. Our experimental system may be useful to address the question of why strawberry plants fail to produce good quality fruit in periods of high temperature. This work is of interest to plant scientists interested in fruit growth and quality, and in plant responses to heat stress.

Technical Abstract: Strawberry fruit contain indole-3-acetic acid (IAA) covalently attached to specific strawberry proteins. Immunoblotting using a specific antibody to IAA-glycine linked to BSA detected IAA proteins in both achenes and receptacles. Protein-conjugated IAA accounts for the majority of the total IAA pool tissue in both the achenes and receptacle. The IAA-glycine antibody detected a single band in receptacle tissue and multiple bands in achenes. Proteins in a wide, immunoreactive, band from 2D PAGE analysis were previously subjected to in-gel trypsin digestion followed by analysis of the tryptic peptides by LC-MS/MS. Fragment analysis tentatively identified the IAA-protein as either an ATP-synthase or, possible, a chaperonin related to the hsp60 class of proteins. PAGE of proteins from a developmental series of fruit of the commercially grown octoploid strawberry (F. x ananassa L. ‘Ovation’) and from the octoploid progenitor species F. virginiana L. ‘LH50-4’ indicated that the IAA-protein is more abundant early in fruit development than in mature unripe berries. In contrast, the opposite pattern, low in early development but increasing with maturity, was observed in the other octoploid progenitor, F. chiloensis ‘Scotts Creek’. Tissue immunoprinting showed that IAA-proteins were present uniformly in the cortex and achenes in very young fruit, but were localized in epidermal tissue and achenes in nearly mature unripe fruit. The IAA modified protein in fruit tissue is the first such protein described with predicted functions and the first IAA protein described in developing and actively growing plant tissues.