The origin and functional transition of P34.

P34, a storage protein and major soybean allergen, has undergone a functional transition from a cysteine peptidase to a syringolide receptor. An exploration of the evolutionary mechanism of this functional transition is made. To identify homologous genes of P34, syntenic network was constructed using syntenic relationships from the Plant Genome Duplication Database. The collected homologous genes, along with SPE31, a highly homologous protein to P34 from the seeds of Pachyrhizus erosus, were used to construct a phylogenetic tree. The results show that multiple gene duplications, exon shuffling and following granulin domain loss and some critical point mutations are associated with the functional transition. Although some tests suggested the existence of positive selection, the possibility that random fixation under relaxation of purifying selection results in the functional transition is also supported. In addition, the genes Glyma08g12340 and Medtr8g086470 may belong to a new group within the papain family.