Title : NRT1/PTR FAMILY (NPF) gene pleiotropically regulates myricetin content and seed number/silique in rapeseed (Brassica napus L.) under drought stress
Rapeseed (Brassica napus L.), which is the second leading oil crop in the world accumulates flavonoids and provides valuable nutrients for human health. Development of drought tolerance rapeseed characterized by high flavonoids content and high yield is an important goal of rapeseed breeding programs worldwide. In this study, an association panel containing 119 rapeseed germplasms was used for genome-wide association studies (GWASs) of genetic loci associated with flavonoids and yield-related traits under well water and drought stress conditions for three years. In addition, transcriptome analysis was performed from seeds and leaves using four rapeseed cultivars with contrasting grain yield and flavonoids content. Results showed that seven significant signals (P < 10-7) associated with both myricetin and seed number/silique were detected on chromosome A09 (15126743- 22810667bp) under drought stress conditions, which explained 35.34% and 16.18% of the phenotypic variances of the tested traits, respectively. The Chr9: 15663349 (A/G), Chr9: 15664117 (A/G), Chr9: 15685531 (A/G) and Chr9: 15687636 (A/G) pleiotropic SNPs in LD block, were located ~200 kb upstream and downstream of two members of NRT1/PTR FAMILY (NPF) genes, NPF8.3 and NPF8.4. Up-regulation of the NPF8.3 and NPF8.4 was observed in both high-yield and high-flavonoids cultivars.
In the Kyoto Encyclopedia of Genes and Genomes analysis (KEGG) analysis, we found that NPF was from the amino acid metabolism, stress signals and biosynthesis of other secondary metabolites. We examined the expression profiles of NPF genes in the rapeseed vegetative and reproductive organs by transcriptome analysis, and the results showed that this gene was expressed abundantly and specifically in seeds. Moreover, our results suggested that drought tolerance could result in a series of changes in cell metabolism, biosynthesis and signal pathways, thereby promoting plant growth under drought. Particularly, the changes of phytohormone and flavonoid metabolism induced by drought might contribute to the promotion of rapeseed growth and grain yield. These results provide information for understanding the genetic basis of drought tolerance and further studies on the identified candidate genes should illuminate mechanisms of drought tolerance and provide tools for designing drought-tolerant and high-flavonoid rapeseed cultivars.