The Spermine Synthase OsSPMS1 Regulates Seed Germination, Grain Size, and Yield

Abstract

Polyamines, including putrescine, spermidine, and spermine, play essential roles in a wide variety of prokaryotic and eukaryotic organisms. Rice (<i>Oryza sativa</i>) contains four putative spermidine/spermine synthase (SPMS)-encoding genes (<i>OsSPMS1</i>, <i>OsSPMS2</i>, <i>OsSPMS3</i>, and <i>OsACAULIS5</i>), but none have been functionally characterized. In this study, we used a reverse genetic strategy to investigate the biological function of <i>OsSPMS1</i> We generated several homozygous RNA interference (RNAi) and overexpression (OE) lines of <i>OsSPMS1</i> Phenotypic analysis indicated that <i>OsSPMS1</i> negatively regulates seed germination, grain size, and grain yield per plant. The ratio of spermine to spermidine was significantly lower in the RNAi lines and considerably higher in the OE lines than in the wild type, suggesting that OsSPMS1 may function as a SPMS. <i>S</i>-Adenosyl-l-methionine is a common precursor of polyamines and ethylene biosynthesis. The 1-aminocyclopropane-1-carboxylic acid (ACC) and ethylene contents in seeds increased significantly in RNAi lines and decreased in OE lines, respectively, compared with the wild type. Additionally, the reduced germination rates and growth defects of OE lines could be rescued with ACC treatment. These data suggest that <i>OsSPMS1</i> affects ethylene synthesis and may regulate seed germination and plant growth by affecting the ACC and ethylene pathways. Most importantly, an <i>OsSPMS1</i> knockout mutant showed an increase in grain yield per plant in a high-yield variety, Suken118, suggesting that <i>OsSPMS1</i> is an important target for yield enhancement in rice.