De novo transcriptome assembly of the fresh-cut white husk of Juglans cathayensis Dode: Insights for enzymatic browning mechanism of fresh-cut husk of walnut

Chinese walnut (Juglans cathayensis Dode) is an excellent breeding germplasm to improve certain economically essential traits of Persian walnut (Juglans regia L.). However, only a few genomic characterization studies of the Chinese walnut have been reported and made available to the public for walnut breeding practice. In the present study, we found new walnut germplasm from wild Juglans cathayensis Dode population, characterized by white husk and lack of browning. We compared the transcriptome between the fresh-cut browning (control) and white husks of the Chinese walnut using Illumina HiSeq 4000 platform. A total of 39,234 unigenes, with an average length of 1854 bp, were obtained from the combined clean reads of both husks, and 2,683 differentially expressed genes (DEGs) were identified. Gene annotation analyses revealed that all unigenes were annotated in at least one of the five databases analyzed. We also determined eight enzymatic browning-related DEGs including two PAL genes, one CHS gene, two CL4 genes, two PPO genes, and one SOD gene. In addition, one WRKY transcription factor was differentially regulated in both samples. Thus, our study identifies potential genes of Chinese walnut associated with enzymatic browning and provides a basis for future molecular studies and improvement of the J. regia strain.