Evaluation of the early defoliation trait and identification of resistance genes through a comprehensive transcriptome analysis in pears

Abstract

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.

Keywords

• pear
• early defoliation
• resistance and susceptibility evaluation
• RNA-seq
• WRKY
• ERF