Physiological and transcriptomic analysis of postharvest Jiashi melon at different storage temperatures

Abstract

Low temperature storage prolongs the postharvest life of various fresh fruit and vegetables. However, tropical fruit may suffer from cold stress during storage. Here, Jiashi melons was stored at 3 °C, and 0.5 °C for a period of 36 days, with storage at 21 °C serving as a control. Rotting was delayed at the lower temperatures compared to the control. Storage at 21 °C resulted in more severe weight loss and a high rotting rate. By day 36, the weight loss rate as a result of moisture reduction reached 11% in the control, but only 8% at the lower temperatures. Chilling injury was observed at both low temperatures over time, but its onset was later for storage at 3 °C. The fruit stored at 3 °C also scored better for rotting rate, weight loss rate, and a chilling injury index than fruit stored at 0.5 °C. Storage at 3 °C was associated with higher activity of peroxidase (POD), catalase (CAT), fatty acid desaturase (FAD), and adenosine triphosphatase (ATPase). The transcriptomes of the fruit were sequenced for the time points 0 d, 12 d and 24 d at all three storage temperatures. This identified a total of 415 co-expressed differential genes that are mainly involved in regulation of transcription, signal transduction, response to stress, lipid metabolism and other processes. The findings were corroborated by targeted RT-qPCR analysis. The expression levels of differentially expressed genes (DEGs) indicated that storage at 3 °C induced overexpression of the early cold-responsive genes ICE1 and calcium-dependent protein kinase (CDPK). Extended storage at 3 °C reduced the damage of low-temperature induced oxidative stress and altered lipid metabolism that otherwise would negatively affect cell membrane functions, so that cell homeostasis was maintained for longer. This was enabled by increased expression of MYB, auxin response factor, heat shock protein (HSPs), FAD synthetase and ATPase. This study provides insights in the molecular responses of Jiashi melon towards cold stress, and provides a theoretical basis for the development of new storage and preservation technologies.