Bet v 1-related protein are widely distributed among vascular plants. The family was classyfied by sequence similarity into three subfamilies . The largest of them contains the pathogenesis-related protein family PR-10 . The expression of these proteins is either induced by pathogen attack or abiotic stress or developmentally regulated. PR-10 proteins are expressed in high concentrations in reproductive tissues such as pollen, seeds and fruits. The biological function of these proteins is still unclear. X-ray crystallography and ligand-binding studies suggest a role as steroid hormone carriers . Other studies point to a ribonuclease activity . The other two subfamilies are a group of major latex proteins and ripening-related proteins first described in the latex of opium poppy  and a small family of proteins containing members with S-norcoclaurin synthase activity, enzymes involved in alkaloid biosynthesis .
The major birch pollen allergen, Bet v 1, is a member of the PR-10 family. Closely-related, cross-reactive allergens were found in the pollen of other trees from the order Fagales such as hazel, alder, and chestnut. Many birch pollen-allergic patients show allergic reactions to various fruits and vegetables, which are caused by IgE cross-reactivity between Bet v 1 and homologous allergens from plant foods . Most Bet v 1-related food allergens were found in members of certain plant families: Rosaceae (apple, pear, stone fruits), Apiaceae (celery, carrot), and Fabaceae (soybean, peanut).
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