Transcriptome Analysis of ‘Haegeum’ Gold Kiwifruit Following Ethylene Treatment to Improve Postharvest Ripening Quality

Abstract

Fruit ripening involves changes in physical, physiological and metabolic activities through the actions of enzymes and regulatory genes. This study was initiated to identify the genes related to the ripening of kiwifruit. Gold ‘Haegeum’ kiwifruit is a yellow-fleshed kiwifruit cultivar usually used for fresh marketing. The fruit is harvested at a physiologically mature but unripe stage for proper storage, marketing distribution and longer shelf life. To identify the differentially expressed genes (DEGs) during ripening, fruit treated with ethylene were compared with control fruit that ripened naturally without ethylene treatment. Firmness, respiration rate, ethylene production rate, total soluble solids (TSS), titratable acidity (TA), brix acid ratio (BAR) and overall acceptability were taken during the study as fruit ripening indicators. Total mRNAs were sequenced by Illumina high-throughput sequencing platform and the transcriptome gene set was constructed by de novo assembly. We identified 99,601 unigenes with an average length of 511.77 bp in transcriptome contigs. A total of 28,582 differentially expressed unigenes were identified in the ethylene treatment vs. control. Of these 28,582 unigenes, 13,361 and 15,221 genes were up- and downregulated, respectively, in the treated fruit. The results also showed that 1682 and 855 genes were up- and downregulated, respectively, more than 2-fold at p < 0.05 in fruit treated with ethylene as compared with the control fruit. Moreover, we identified 75 genes showing significantly different expression; 42 were upregulated, and 33 were downregulated. A possible category of the identified ripening-related genes was also made. The findings of this study will add to the available information on the effect of ethylene treatment on ripening and the related changes of kiwifruit at the genomic level, and it could assist the further study of genes related to ripening for kiwifruit breeding and improvement.