The expression of OsPSK5, a gene encoding the phytosulfokine-α precursor, regulates seed vigor in rice (Oryza sativa)

The molecular mechanisms regulating seed vigor have attracted significant attention. This study confirmed the expression of OsPSK5, a gene encoding the phytosulfokine (PSK-α) precursor, regulates seed vigor in rice. Subcellular localization analysis showed that OsPSK5 was localized in the Golgi apparatus. Compared with wild-type rice, grain size and seed vigor were significantly decreased and reactive oxygen species (ROS) levels were elevated in ospsk5 mutants, but no significant differences of these traits were observed in OsPSK5-overexpression lines. Complementation of the ospsk5-1 mutant with OsPSK5 restored seed vigor to the wild-type level. The endogenous PSK content of ospsk5-1 seeds was significantly lower, while that in seeds of ospsk5-2 null mutant, OsPSK5-overexpression lines, and complementation lines were either equivalent to or significantly higher than that of wild-type seeds. Additionally, exogenous PSK-α treatment markedly promoted seed viability and callus induction in ospsk5-1 mutant seeds. Transcriptome and metabolome assays revealed that differential expression of OsPSK5 resulted in the differential expression of genes related to the biosynthesis and catabolism of cytokinins, gibberellins, abscisic acid, and polyphenolic compounds, leading to the levels of these secondary metabolites to vary between seeds of different genotypes. As a result, the expression of OsPSK5 may involve in rice seed vigor through modulating the biosynthesis and metabolism of PSK-α, other plant hormones, polyphenols, and ROS homeostasis etc.