Comprehensive genomic analysis of theRNase T2gene family in Rosaceae and expression analysis inPyrus bretschneideri

RNase T2s exist widely in eukaryotes and prokaryotes, playing various physiological roles in plants. At present, the genomes of Chinese white pear and six other Rosaceae fruit crops have been sequenced. However, no comprehensive analysis has investigated the evolutionary characteristics of theRNase T2family in Rosaceae species. Here, 93RNase T2s were identified in seven Rosaceae species (Pyrus bretschneideri,Rubus occidentalis,Fragaria vesca,Malus domestica,Prunus persica,Prunus avium, andPrunus mume). On the basis of phylogenetic analysis and structural characteristics, theRNase T2family can be divided into four classes (I, II, III, and IV). Class IV is a new class first identified among seven Rosaceae species. Intron-exon analysis further revealed a homologous intron inRNase T2s except for class IV. Although purifying selection was the major force acting on theRNase T2family, some positively selected sites and protein regions were still found in class IV sequences by using PAML and sliding windows. Tandem and proximal gene duplications made a major contribution to the expansion of thePbrRNase T2family. Expression analysis identified somePbrRNase T2genes highly expressed in pear and several transcription factors that might regulate these genes. In conclusion, the study of theRNase T2family in seven Rosaceae species will help us to better understand the molecular evolution ofRNase T2genes and facilitate further functional analysis in the future.