Transcriptomic and physiological analysis reveals crucial biological pathways associated with low-temperature stress in Tunisian soft-seed pomegranate (Punica granatum L.)

ABSTRACTLow temperature severely affects the growth of pomegranate in the early spring during the production process under protected cultivation. To understand the molecular responses to cold stress in Tunisian soft-seed pomegranate, this study investigated the transcriptome profiles and physiological changes of pomegranate leaves exposed to cold stress (6 °C) and freezing stress (0°C). Some potential cold response/resistance genes involved in plant hormone signal transduction, photosynthetic systems and carbon fixation in the C4 pathway, and sucrose and galactose metabolism were identified. In addition, an analysis of physiological indicators indicated that both stresses caused cell membrane damage; the accumulation of soluble sugar, soluble protein and proline; and the occurrence of photoinhibition owing to the damage in photosynthetic apparatus and the decrease in light energy conversion efficiency and electron transfer rate as shown by the decrease in net photosynthetic rate [Pn], potential maximum photochemical efficiency of PSII [Fv/Fm], actual photochemical efficiency of PSII [YII] and photochemical quenching coefficient [qP], and the effect was much moresevere in pomegranate under freezing stress. This study results offer useful information to understand the molecular mechanism of pomegranate response to cold stress and also lay a foundation for the selection of major candidate genes to conduct molecular breeding for cold tolerance in pomegranate.