Cynara cardunculus (L.) seeds transcriptome sequencing

The association among environmental cues, ethylene response, ABA signalling and reactive oxygen species (ROS) homeostasis in the seed dormancy termination process is nowadays well-established in many species. Alternating temperatures are recognized as one of the main environmental signal determining a quick promotion of dormancy relief, but their underlying mechanisms are scarcely known. Wild cardoon achenes poorly germinated at constant temperature of 20, 15 or 10 C, whereas germination was substantially improved at alternating temperatures of 20/10 C (above 80%). Using a RNA-seq approach, we identified 23,640 and annotated 13,783 gene transcripts expressed in achenes exposed to constant or alternating temperatures. Among them we identified transcripts homologous to key-genes involved in the regulation of dormancy termination. Alternating temperatures sharply increased the expression of ACO1, ERS1, RBOH, genes related to ethylene synthesis and signalling and ROS synthesis. Accordingly, a higher ethylene content was confirmed via gas chromatography. In contrast, CAT gene expression (associated with ROS degradation) was reduced suggesting a precise equilibrium among ROS synthesis and degradation. Use of ethylene inhibitors, NAD(P)H oxidase inhibitor and ROS scavengers reduced germination at 20/10 C. Conversely, the presence of methylviologen and a peroxidase inhibitor increased germination at constant temperatures. Taken together, these results evidence that exposure to alternating temperatures elicits a specific ROS amount production and the activation of ethylene metabolism that may promote dormancy termination.