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

Author
item PARK, SEIJIN - U. MINN
item COHEN, JERRY - U. MINN
item Slovin, Janet

Submitted to: Planta
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/2/2006
Publication Date: 5/15/2006
Citation: Park, S., Cohen, J., Slovin, J.P. 2006. Strawberry fruit protein with a novel indole-acyl post-translational modification. Planta. 224: 1015-1022

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 this hormone is produced by developing strawberry “seeds”, which causes the fruit to grow and also affects ripening. We were able to make a tentative identification of the protein to which the hormone is attached in strawberry fruit. The protein appears to be involved in resistance to heat stress. Thus 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 plant responses to heat stress.

Technical Abstract: Achenes and receptacle tissue of Fragaria vesca cultivar Yellow Wonder were shown to contain conjugated indole-3-acetic acid (IAA) that was not soluble in organic solvents and yielded IAA after strong alkaline hydrolysis, suggestive of IAA attached to plant proteins. This solvent insoluble conjugated IAA accounted for between 0.4 and 4 ng of IAA per gram fresh weight of tissue in both achenes and receptacles. To investigate this strawberry conjugate class further, a polyclonal antibody was produced to IAA-glycine attached to BSA that detected neutral indole acid esters, monocarboxylic-amino acid IAA conjugates and IAA-proteins. Using immunoblotting, both achenes and receptacles of strawberry were shown to have primarily an immuno-detectable band at 79 kDa. Two-dimensional polyacrylamide gel electrophoresis yielded a wide band that was analyzed by LC-MS/MS analysis following in-gel typsin digestion. The strawberry IAA-protein was tentatively identified by peptide fragment analysis as either a chaperonin related to the hsp60 class of proteins or, alternatively, an ATP-synthase. This is one of the first reports of an IAA modified protein in fruit tissue and is the first indication that proteins with functions related to stress responses might be modified by IAA and present in developing plant tissues.