Comparative physiological and metabolomic analyses reveal natural variations of tulip in response to storage temperatures.

MAIN CONCLUSION: Three tulip cultivars were screened out with successful bloom after a short-term cold treatment, and the differential responses to postharvest cold treatment were analyzed between two contrasting tulip cultivars. Tulip is one of the most important ornamental bulbous plants in the world. A precious precooling treatment during bulb postharvest is required for optimal floral stalk elongation and flower development in tulip. In this study, the naturally growing and flowering variations of tulip to storage temperatures were analyzed after long-term cold (LTC) and short-term cold (STC) treatments. Three cultivars were screened out with successful blooming after STC, which included 'Dow Jones' (DJ), 'Van Eijk' (VE) and 'World's Favourite' (WF) (5 °C for 2 weeks). Comparative analysis revealed that DJ cultivar maintained normal and intact reproductive organs under STC condition, while the 'Orange Emperor' (OE) cultivar, which failed blooming after STC treatment, showed gradually destroyed reproductive organs under STC condition. In addition, the DJ cultivar accumulated lower ROS levels and higher antioxidant enzyme activities, as well as significantly higher contents of total primary metabolites than OE to maintain normal shoot growth and floral organ development under STC condition. The relative expression levels of genes involved in vernalization and/or flower time regulation in DJ were significantly higher than those in OE after STC treatment. This study provides new insights into understanding the underlying mechanism of natural variation of tulip cultivars during postharvest storage treatment.

Identification of heat-responsive genes in carnation (Dianthus caryophyllus L.) by RNA-seq.

Carnation (Dianthus caryophyllus L.) is an important flower crop, having substantial commercial value as a cut-flower due to the long vase-life and wide array of flower colors and forms. Standard carnation varieties perform well under cool climates but are very susceptible to high temperatures which adversely affect the yield and the quality of the cut-flowers. Despite several studies of carnation contributing to the number of expressed sequence tags (ESTs), transcriptomic information of this species remains very limited, particularly regarding abiotic stress-related genes. Here, transcriptome analysis was performed to generate expression profiles of heat stress (HS)-responsive genes in carnation. We sequenced a cDNA library constructed with mixed RNA from carnation leaves subjected to 42°C HS (0, 0.5, 1, and 2 h) and 46°C HS (0.5, 1, and 2 h), and obtained 45,604,882 high quality paired-end reads. After de novo assembly and quantitative assessment 99,255 contigs were generated with an average length of 1053 bp. We then obtained functional annotations by aligning contigs with public protein databases including NR, SwissProt, KEGG, and COG. Using the above carnation transcriptome as the reference, we compared the effects of high temperature treatments (42°C: duration 0.5, 2, or 12 h) delivered to aseptic carnation seedlings, relative to untreated controls, using the FPKM metric. Overall, 11,471 genes were identified which showed a significant response to one or more of the three HS treatment times. In addition, based on GO and metabolic pathway enrichment analyses, a series of candidate genes involved in thermo-tolerance responses were selected and characterized. This study represents the first expression profiling analysis of D. caryophyllus under heat stress treatments. Numerous genes were found to be induced in response to HS, the study of which may advance our understanding of heat response of carnation.