Nitric oxide affects seed oil accumulation and fatty acid composition through protein S-nitrosation

Nitric oxide (NO) has been implicated as a key signaling molecule involved in a wide spectrum of plant developmental and stress responses. Here, we found that NO also played important role in seed oil content and fatty acid composition. RNAi silencing Arabidopsis thaliana S-nitrosoglutathione reductase 1 (GSNOR1) gene led to higher NO content and up to 5.3% reduction of seed oil content. In contrast, nitrate reductase double mutant nia1nia2 led to an increase of seed oil content by 2.6%, compared to the wild type plant. Moreover, the levels of palmitic acid (C16:0), linoleic acid (C18:2) and linolenic acid (C18:3) were higher, whereas the levels of stearic acid (C18:0), oleic acid (C18:1) and arachidonic acid (C20:1) decreased in the seeds of GSNOR1 RNAi lines. The effects of NO on seed oil content and fatty acid composition were also demonstrated with rapeseed embryos cultured in vitro with NO donor Sodium Nitroprusside (SNP) and NO inhibitor NG-Nitro-L-arginine Methyl Ester (L-NAME). Similar results with that of Arabidopsis were obtained. Compared to non-treated embryo control, the oil contents were decreased by 1.95% and 4.69% in 10µM and 20µM SNP-treated embryos and increased by 1.66% and 2.43% in 200µM and 400µM L-NAME-treated embryos respectively. The relative quantities of C16:0, C18:2 and C18:3 were significantly higher, whereas C18:1 level decreased markedly in rapeseed embryos treated with SNP. Proteomics and transcriptome analysis revealed that three S-nitrosated proteins (PKp2, LACS4, and SSI2) and some key genes involved in oil synthesis were differentially regulated in SNP treated embryos, suggesting that NO regulated seed oil content and fatty acid composition. The seed oil content increase in Arabidopsis and rapeseed was further obtained by spraying L-NAME directly on developing siliques. These results suggested that regulating NO level could be a novel approach to increase seed oil content in oil crops during cultivation in addition to marker-assisted selection breeding and genetically modified breeding.

Keywords: GSNOR1 RNAi; NO; PKp; S-nitrosation; embryo culture; oil content.