Comparative metabolomics and transcriptomics of pistils, stamens and pistilloid stamens widen key knowledge of pistil and stamen development in wheat

To examine the role of metabolites in wheat stamen and pistil development, metabolomic analyses of pistilloid stamens (PS), pistils (P), and stamens (S) from a novel wheat mutant homologous transformation sterility-1 (HTS-1) and controls from their sib-line CSTP were conducted using base gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-mass spectrometry (LC-MS). Then, the metabolomic data were integrated with previously published transcriptomic data and analysed. In total, 141 annotated metabolites were determined from P, PS and S tissues by comparison with reference standards. A total of 90, 93 and 18 different metabolites were identified in S vs. PS, S vs. P and P vs. PS, respectively. Among the different metabolites, 80 may be associated with stamen and pistil growth. Using integration evaluations of both the previous transcriptome data and the 80 various metabolites, we found two perturbed pathways that significantly affect flower development in plants, namely, the phenylpropanoid biosynthesis and cysteine and methionine metabolism. The ethylene synthesis pathway, one key branch of the cysteine and methionine metabolic pathways, could have a pivotal role in pistillody growth involving HTS-1. We found two key enzyme genes in the ethylene synthesis pathway (the SAM synthase gene and the ACC synthase gene) that have higher expression levels in stamens than in pistilloid stamens or pistils. We speculate, that the decrease in ethylene content during stamen development leads to pistillody traits in HTS-1. This study helps elucidate the molecular mechanisms underlying stamen and pistil growth in wheat.