Transcriptomic changes in Cucurbita pepo fruit after cold storage: differential response between two cultivars contrasting in chilling sensitivity

F Carvajal,R Rosales,J Cañizares,F Palma,M Jamilena,D Garrido,S Manzano

doi:10.1186/s12864-018-4500-9

F Carvajal, R Rosales + Show 5 more

Open Access

https://doi.org/10.1186/s12864-018-4500-9

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Abstract

BackgroundZucchini fruit is susceptible to chilling injury (CI), but the response to low storage temperature is cultivar dependent. Previous reports about the response of zucchini fruit to chilling storage have been focused on the physiology and biochemistry of this process, with little information about the molecular mechanisms underlying it. In this work, we present a comprehensive analysis of transcriptomic changes that take place after cold storage in zucchini fruit of two commercial cultivars with contrasting response to chilling stress.ResultsRNA-Seq analysis was conducted in exocarp of fruit at harvest and after 14 days of storage at 4 and 20 °C. Differential expressed genes (DEGs) were obtained comparing fruit stored at 4 °C with their control at 20 °C, and then specific and common up and down-regulated DEGs of each cultivar were identified. Functional analysis of these DEGs identified similarities between the response of zucchini fruit to low temperature and other stresses, with an important number of GO terms related to biotic and abiotic stresses overrepresented in both cultivars. This study also revealed several molecular mechanisms that could be related to chilling tolerance, since they were up-regulated in cv. Natura (CI tolerant) or down-regulated in cv. Sinatra (CI sensitive). These mechanisms were mainly those related to carbohydrate and energy metabolism, transcription, signal transduction, and protein transport and degradation. Among DEGs belonging to these pathways, we selected candidate genes that could regulate or promote chilling tolerance in zucchini fruit including the transcription factors MYB76-like, ZAT10-like, DELLA protein GAIP, and AP2/ERF domain-containing protein.ConclusionsThis study provides a broader understanding of the important mechanisms and processes related to coping with low temperature stress in zucchini fruit and allowed the identification of some candidate genes that may be involved in the acquisition of chilling tolerance in this crop. These genes will be the basis of future studies aimed to identify markers involved in cold tolerance and aid in zucchini breeding programs.

Highlights

Zucchini fruit is susceptible to chilling injury (CI), but the response to low storage temperature is cultivar dependent
Transcriptional bases for the differential response of fruit of the two zucchini cultivars to cold storage The principal component analysis (PCA) analysis showed a differential transcriptomic response between cultivars; Sinatra fruit stored at 20 °C were clustered away from fruit stored at 4 ° C, whereas chilled and non-chilled fruit from Natura were grouped together
We propose that the transcription factors identified in our study are promising candidate genes for controlling chilling tolerance in zucchini, especially those induced by low temperature in the coldtolerant cultivar Natura (MYB76-like, CUUC97743; AP2/ ERF-like, CUUC104934; and ZAT10-like, CUUC61049)

Summary

Introduction

Zucchini fruit is susceptible to chilling injury (CI), but the response to low storage temperature is cultivar dependent. Subsequent physiological research revealed many differences between these two cultivars in some metabolic pathways involved in chilling stress and tolerance, confirming that Natura and Sinatra should be considered tolerant and sensitive cultivars to cold stress, respectively In this sense, Natura fruit has higher soluble sugar content, higher levels of proline, lower content in chilling stress metabolites such as H2O2 or MDA, and higher gene expression and activity of antioxidant defense enzymes, than Sinatra fruit [7, 10, 11]. There is an increasing amount of information concerning the physiology and biochemistry of chilling in zucchini fruit, the molecular mechanisms underlying the response of zucchini fruit to chilling storage is limited to specific molecular pathways, including those of ethylene biosynthesis and signaling [5, 6], enzymatic antioxidant system [12, 13], abscisic acid synthesis and signaling, and polyamine metabolism [3, 7]

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