Cerium nano-oxide promotes cotton (Gossypium hirsutum L.) seed germination by regulating auxin and brassinolide homeostasis and signal transduction in the hypocotyl

Seed priming with engineered nanoparticles can promote seed germination. Herein, we investigated how priming seeds with antioxidant poly(acrylic acid)-coated cerium oxide nanoparticles (PNC, 0.05 mM) impacts seed germination in cotton (Gossypium hirsutum L.). Seed priming with PNC significantly increased cotton hypocotyl elongation by 13 %-37 %, promoting seed germination in pot experiment. Meanwhile, the emergence rate increased by 15 %-16 % with 0.05 mM PNC-seed priming in the field. Transcriptome analysis identified PNC-induced differentially expressed genes (DEGs) related to the phytohormone, auxin (IAA), and brassinosteroid (BR) biosynthesis (e.g. GhTAA1, GhYUCCA, GhALDH, GhGH3, GhCYPs) and signal transduction (e.g. GhSAUR, GhBZR1). Consistently, PNC priming increased the accumulation of IAA (10 %-25 %) and BR (86 %-100 %) in cotton hypocotyls. In addition, PNC enhanced the expression of the xyloglucan endotransglucosylase/hydrolase (XTHs) genes, regulated by SAUR and BZR1 through IAA and BR signaling pathway and critical for cell elongation. Also, the cell lengths of the epidermis, endodermis, xylem, and pith in cotton hypocotyl increased by 21 %, 17 %, 31 %, and 21 %, respectively upon seed priming with 0.05 mM PNC. The results provide insights into the molecular mechanisms of nanoparticles-seed priming enhancement of plant seed gemination.