Comparative phylogenetic analyses of recombinant noroviruses based on different protein-encoding regions show the recombination-associated evolution pattern.

Noroviruses are the major cause of acute gastroenteritis worldwide, and recombination is recognized as the important mechanism for its continuous emergence. In this study, for the common GII.P12 and GII.3 recombinants, phylogenetic relationships based on different proteins in three ORFs were comparatively analyzed, focusing on the influence of intergenic recombination. By using newly designed primers, genomes of two GII.P12/GII.3 Guangzhou recombinants were firstly amplified. Combined with other reported sequences of GII.P12_ORF1 (n = 20), GII.3_ORF2 (n = 131), GII.3_ORF3 (n = 36), all GII.P12 and GII.3 strains could be divided into 6, 8, and 7 clusters based on different ORFs, which showed an obvious recombination-associated and temporally sequential evolution pattern (with the exception of GII.P12/GII.13 recombinants). Based on multiple alignments, 126 informative sites were identified in three ORFs (44, 54, and 28), and four proteins (p48, p22, VP1, and VP2) were found under positive selection. Furthermore, by using homology modeling, predicted epitopes were mapped on the P proteins of seven GII.3 representative strains, without one (Epi: 353-361) specific to the GII.4 VA387 strain. In summary, via the genome analyses, phylogenetic relationships of GII.P12 and GII.3 recombinants based on the different proteins presented a special temporally sequential evolution process associated with their recombinant types.