Transcriptome analysis suggests the role of expansin genes in the improved germination of sunflower (Helianthus annuus L.) seeds after hydropriming

Sunflower (Helianthus annuus L.) is widely utilized for seed oil production. Priming seeds prior to sowing is a technique used to enhance the germination rate and uniformity of seedling growth. Priming times of 6 and 18 h were selected to be the optimal and extended durations, respectively. Three biological replicates per treatment were used for next-generation sequencing via the Illumina platform. In this study, priming conditions decreased the time to 50% radicle emergence, implying earlier and more uniform germination without affecting the final germination percentage. Transcriptome analysis identified 6171 differentially expressed genes (DEGs) for 0-6 h, 7241 DEGs for 0-18 h, and 1527 DEGs for 6-18 h. The number of expressed DEGs during the early hours of priming exceeded those identified during the extended priming time, suggesting more metabolic processes were taking place in the earlier priming period. Noteworthy DEGs are related to stress responses, the biosynthesis of metabolites, and the activation of antioxidants and phytohormones. Moreover, these DEGs were significantly enriched in translation, metabolic processes, and biosynthesis for the priming times of 0-6 h and 0-18 h, whereas anaerobic respiration, detection of hypoxia, and lipid transport were differentially expressed between 6 and 18 h. Furthermore, expansin genes, namely, EXPA1, EXPA9, EXPA15, EXLA3, and EXP/Lol pI 3B GAG-pre-integrase domain, were significantly expressed. These expansins are cell wall-loosening proteins that are involved in the processes of physiological development in higher plants, including seed germination. The data obtained in this study contribute toward deciphering the molecular mechanisms associated with seed priming in sunflower seeds.