Molecular mechanisms involved in postharvest chilling tolerance of pomegranate fruit

Abstract Cold storage of pomegranates is essential for prolonging postharvest storage and for the implementation of cold‐quarantine insect disinfestation treatments required for international trading. However, pomegranates are chilling sensitive; they may develop chilling injuries upon exposure to unfavorable low temperatures. In this mini‐review, we summarize molecular data obtained from three different RNA Seq transcriptome analyses of responses of pomegranate fruits to cold storage. These experiments included comparisons among the transcriptomic responses following a 2‐week exposure to 1 °C in three different model systems: 1) unconditioned chilling‐sensitive fruits versus relatively chilling‐tolerant low‐temperature‐conditioned fruits; 2) chilling‐sensitive early harvested fruits versus relatively chilling‐tolerant late‐harvested ones; and 3) chilling‐sensitive ‘Ganesh’ variety versus the relatively chilling‐tolerant ‘Wonderful’ variety. Comparisons among differentially expressed transcripts that were exclusively and significantly up‐regulated in the relatively chilling‐tolerant fruits in all three model systems enabled identification of 573 common chilling tolerance‐associated genes in pomegranates. Functional categorization and classification of the differentially expressed transcripts revealed several regulatory, metabolic, and stress‐adaptation pathways that were uniquely activated in response to cold storage in relatively chilling‐tolerant fruits. More specifically, we identified common up‐regulation of transcripts involved in activation of jasmonic acid and ethylene hormone biosynthesis and signaling, stress‐related transcription factors, calcium and MAPK signaling, starch degradation and galactinol and raffinose biosynthesis, phenol biosynthesis, lipid metabolism, and heat‐shock proteins. We hypothesized these pathways to be involved in imparting chilling tolerance to pomegranate fruits. © 2019 Society of Chemical Industry