Spatio-temporal distribution of phenolamides and the genetics of natural variation of hydroxycinnamoyl spermidine in rice.

Phenolamides constitute a diverse class of secondary metabolites that are found ubiquitously in plants and have been implicated to play important role in a wide range of biological processes such as plant development and defense. However, spatio-temporal accumulation patterns of phenolamides in rice, one of the most important crops, are not available so far, and no gene responsible for the phenolamides biosynthesis has been identified in this species. In this report, we report here the comprehensive metabolic profiling and natural variation analysis of phenolamides in a collection of rice germplasm using an LC-MS-based targeted metabolomics method. Spatio-temporal controlled accumulations were observed for most phenolamides, together with their differential accumulations between the two major subspecies of rice. Further metabolic genome-wide association study (mGWAS) in rice leaf and the in vivo metabolic analysis of the transgenic plants identified Os12g27200 and Os12g27254 as two spermidine hydroxycinnamoyl transferases that might be underlying the natural variation of levels of spermidine conjugates in rice. Our work demonstrates 'gene-to-metabolite' analysis by mGWAS provides a useful tool for functional gene identification and omics-based crop genetic improvement.