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

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.