The red coloring of pear fruits is mainly caused by anthocyanin accumulation.  Red sport, represented by the green pear cultivar ‘Bartlett’ (BL) and the red-skinned derivative ‘Max Red Bartlett’ (MRB), is an ideal material for studying the molecular mechanism of anthocyanin accumulation in pear.  Genetic analysis has previously revealed a quantitative trait locus (QTL) associated with red skin color in MRB.  However, the key gene in the QTL and the associated regulatory mechanism remain unknown.  In the present study, transcriptomic and methylomic analyses were performed using pear skin for comparisons between BL and MRB.  These analyses revealed differential PcHY5 DNA methylation levels between the two cultivars; MRB had lower PcHY5 methylation than BL during fruit development, and PcHY5 was more highly expressed in MRB than in BL.  These results indicated that PcHY5 is involved in the variations in skin color between BL and MRB.  We further used dual luciferase assays to verify that PcHY5 activates the promoters of the anthocyanin biosynthesis and transport genes PcUFGT, PcGST, PcMYB10 and PcMYB114, confirming that PcHY5 not only regulates anthocyanin biosynthesis but also anthocyanin transport.  Furthermore, we analyzed a key differentially methylated site between MRB and BL, and found that it was located in an intronic region of PcHY5.  The lower methylation levels in this PcHY5 intron in MRB were associated with red fruit color during development, whereas the higher methylation levels at the same site in BL were associated with green fruit color.  Based on the differential expression and methylation patterns in PcHY5 and gene functional verification, we hypothesize that PcHY5, which is regulated by methylation levels, affects anthocyanin biosynthesis and transport to cause the variations in skin color between BL and MRB.

Early defoliation, which usually occurs during summer in pear trees, is gradually becoming a major problem that poses a serious threat to the pear industry in southern China.  However, there is no system for evaluating the responses of different cultivars to early defoliation, and our knowledge of the potential molecular regulation of the genes underlying this phenomenon is still limited.  In this study, we conducted field investigations of 155 pear accessions to assess their resistance or susceptibility to early defoliation.  A total of 126 accessions were found to be susceptible to early defoliation, and only 29 accessions were resistant.  Among them, 19 resistant accessions belong to the sand pear species (Pyrus pyrifolia).  To identify the resistance genes related to early defoliation, the healthy and diseased samples of two sand pear accessions, namely, the resistant early defoliation accession ‘Whasan’ and the susceptible early defoliation accession ‘Cuiguan’, were used to perform RNA sequencing.  Compared with ‘Cuiguan’, a total of 444 genes were uniquely differentially expressed in ‘Whasan’.  Combined with GO and KEGG enrichment analyses, we found that early defoliation was closely related to the stress response.  Furthermore, a weighted gene co-expression network analysis revealed a high correlation of WRKY and ethylene responsive factor (ERF) transcription factors with early defoliation resistance.  This study provides useful resistant germplasm resources and new insights into potentially essential genes that respond to early defoliation in pears, which may facilitate a better understanding of the resistance mechanism and molecular breeding of resistant pear cultivars