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Jin Jiao, Xing Liu, Juyou Wu, Guohua Xu and Shaoling Zhang

Mitogen-activated protein kinase (MAPK) cascades are universal signal-transduction modules, but the available information is limited in pear (Pyrus). In this study, 87 MAPK genes were identified from five Rosaceae species: chinese white pear (Pyrus ×bretschneideri cv. Dangshansuli), peach (Prunus persica), apple (Malus domestica), strawberry (Fragaria vesca), and plum (Prunus mume), 23 of which came from chinese white pear, designated as PbrMAPK. Based on the phylogenetic analysis and the architectures of conserved protein motifs of these gene sequences, MAPK family genes of five Rosaceae species were classified into two primary types (I and II) or four groups (Classes A–D). We have indicated that both segment and tandem duplications significantly contributed to the expansion of the MAPK family in Rosaceae by analysis of genomic evolution. In chinese white pear pollen, the expression analysis revealed that all PbrMAPKs could respond to temperature stresses (high/low temperature) and phytohormones, except PbrMAPK8 and PbrMAPK19 that displayed lower expressions, which suggested that PbrMAPKs play pivotal roles in signal-transduction pathways. In addition, we determined that PbrMAPK13 is located in the nucleus and plasma membranes. The lengths of pollen tubes became shorter when PbrMAPK13 was silenced by antisense oligonucleotide transfection. Our results provided an evolutionary foundation and functional characterization for MAPK gene families in chinese white pear and other plant species so as to elucidate their biological roles.

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Shutian Tao, Danyang Wang, Cong Jin, Wei Sun, Xing Liu, Shaoling Zhang, Fuyong Gao and Shahrokh Khanizadeh

Lignin is the main component of stone cells, and stone cell content is one of the crucial factors for fruit quality in chinese white pear (Pyrus ×bretschneideri). The lignin biosynthesis pathway is complex and involves many enzymatic reactions. Cinnamate-4-hydroxylase [C4H (EC.1.14.13.11)] is an essential enzyme in lignin metabolism. This study was conducted to investigate the effect of bagging on lignin metabolism during fruit development in chinese white pear. The study showed that bagging had little effect on stone cell content, lignin content, C4H activity, and C4H gene expression and that there was a positive correlation between C4H gene expression and lignin content as well as stone cell content. Moreover, a full-length complementary DNA (cDNA) encoding C4H (PbrC4H, GenBank accession number KJ577541.1) was isolated from chinese white pear fruit. The cDNA is 1515 bp long and encodes a protein of 504 amino acids. Sequence alignment suggested that the deduced protein belongs to the P450 gene family and that C4H might be located subcellularly in the cell membrane. The results indicate that bagging cannot change the lignin and stone cell content significantly and that C4H catalyzes a step in lignin biosynthesis. These findings provide certain theoretical references and practical criteria for improving the quality of chinese white pear.