Transcriptome analysis to elucidate hexanal's mode of action in preserving the post-harvest shelf life and quality of banana fruits (Musa acuminata)

Banana is a climacteric fruit whose ripening once initiated is irreversible and proceeds very fast making the fruits highly perishable. Application of various post-harvest technologies has been shown to slow down the ripening process in climacteric fruits such as banana. One of these technologies is hexanal, a naturally occurring compound that delays the ripening process in banana fruits without compromising the quality. As the molecular mechanisms underlying the mode of action of hexanal in delaying ripening are yet to be elucidated, we undertook a comparative transcriptomic analysis using banana fruits treated with either hexanal, ethylene or untreated controls. Results of our study show that hexanal significantly delayed the rate of pulp softening throughout the storage period. Sequencing results showed that 776 genes were up-regulated and 2146 were down-regulated upon hexanal treatment while 4 genes were up-regulated and 76 were down-regulated upon ethylene treatment at day one of storage. Additionally, 2423 genes were up-regulated and 2862 were down-regulated upon hexanal treatment while a total of 4820 genes were up-regulated and 5395 were down-regulated upon ethylene treatment at day four. We found that hexanal treatment transiently suppressed the expression of genes involved in ethylene biosynthesis, cell membrane deterioration and cell wall degradation by day four of storage contrary to the observed induction of the same genes in ethylene-treated fruits. The particular genes are; Aminocyclopropane-1-Carboxylic Acid Oxidase, 1-Aminocyclopropane-1-Carboxylic Acid, Phospholipase D, Polygalacturonase, Expansin and Xyloglucan Endotransglucosylase. Later on at day 18 of storage, genes involved in ethylene biosynthesis, cell wall and cell membrane degradation and aroma synthesis were induced in the hexanal-treated fruits. These findings reveal that hexanal works by temporarily suppressing the expression of genes involved in ethylene biosynthesis, cell wall degradation and cell membrane deterioration.