Strawberry (Fragaria × ananassa) contains a major allergen, Fra a 1, which causes oral allergic syndrome. Fra a 1 is a PR-10 homolog that is regulated by environmental conditions. The allergenicity of fruit caused by Fra a 1 may depend on the genotype or growing conditions. We analyzed the Fra a 1.01 transcript levels and Fra a 1.01 protein levels in strawberry fruits of several genotypes across all seasons. In the preliminary rough screening, we selected the line WH1 bearing white fruit and the red-fruited cultivar 'Akihime'. Under the same environmental conditions, there was no significant difference in Fra a 1.01 levels between the two cultivars over several months, suggesting that receptacle color was not indicative of allergenicity caused by Fra a 1.01. Fruits cultivated under the same environmental conditions should be used for comparisons of the allergenicity among genotypes. Both 'Akihime' and WH1 accumulated significantly higher levels of Fra a 1.01 protein in winter than in spring. We investigated the effects of irradiation and low temperature as environmental factors controlling the accumulation of Fra a 1.01 in winter. A shading treatment on fruit did not significantly affect Fra a 1.01 protein accumulation in strawberry fruits. Regarding variations over time, the Fra a 1.01 protein content was higher in fruits harvested at midnight in January than in those harvested at other times and in other months. These findings suggested that the Fra a 1.01 protein accumulates in response to environmental factors such as cold stress.

Fra a 1 is a strawberry allergen that causes oral allergic syndrome. Fra a 1.01 is a major isoform that accumulates abundantly in fruits during the winter season. Here, we tested the hypothesis that Fra a 1.01 responds to environmental factors, such as cold stress. We analyzed transcriptional and translational levels of Fra a 1.01 in strawberry calli and organs under various cold conditions. First, we incubated strawberry (Fragaria × ananassa 'Akihime') calli and post-harvested fruits at low temperatures from several hours to days. Fra a 1.01 did not show significant differences in either gene expression or protein accumulation levels, suggesting that short-term cold treatments did not affect Fra a 1.01 expression. Second, we exposed whole plants to low temperature conditions for ~28 days. Under conditions below 10°C, Fra a 1.01 transcripts were induced gradually throughout the cold treatment (crown and root), or from 2 days to the last day (leaf and fruit). The Fra a 1.01 protein remarkably accumulated in crowns and slightly in fruits after 28 days. Finally, the promoter region of Fra a 1.01e was analyzed to detect tissue-specific expression. The cloned and sequenced promoter included several cis-acting regulatory elements related to cold response. When the Fra a 1.01 promoter region was heterologously expressed in Arabidopsis, the promoter activities, as assessed by GUS staining, were observed mainly around the shoot apices and in roots. Thus, Fra a 1.01 was considered to be expressed in crowns and roots, and was additively induced by cold stress. These organ-specific expressions could be important in elucidating the mechanisms responsible for Fra a 1.01 protein's accumulation in fruits during the winter season.