Abstract
Buckwheat is an important minor crop with pharmaceutical functions due to rutin enrichment in the seed. Seeds of common buckwheat cultivars (Fagopyrum esculentum, Fes) usually have much lower rutin content than tartary buckwheat (F. tartaricum, Ft). We previously found a wild species of common buckwheat (F. esculentum ssp. ancestrale, Fea), with seeds that are high in rutin, similar to Ft. In the present study, we investigated the mechanism by which rutin production varies among different buckwheat cultivars, Fea, a Ft variety (Xide) and a Fes variety (No.2 Pingqiao) using RNA sequencing of filling stage seeds. Sequencing data generated approximately 43.78-Gb of clean bases, all these data were pooled together and assembled 180,568 transcripts, and 109,952 unigenes. We established seed gene expression profiles of each buckwheat sample and assessed genes involved in flavonoid biosynthesis, storage proteins production, CYP450 family, starch and sucrose metabolism, and transcription factors. Differentially expressed genes between Fea and Fes were further analyzed due to their close relationship than with Ft. Expression levels of flavonoid biosynthesis gene FLS1 (Flavonol synthase 1) were similar in Fea and Ft, and much higher than in Fes, which was validated by qRT-PCR. This suggests that FLS1 transcript levels may be associated with rutin accumulation in filling stage seeds of buckwheat species. Further, we explored transcription factors by iTAK, and multiple gene families were identified as being involved in the coordinate regulation of metabolism and development. Our extensive transcriptomic data sets provide a complete description of metabolically related genes that are differentially expressed in filling stage buckwheat seeds and suggests that FLS1 is a key controller of rutin synthesis in buckwheat species. FLS1 can effectively convert dihydroflavonoids into flavonol products. These findings provide a basis for further studies of flavonoid biosynthesis in buckwheat breeding to help accelerate flavonoid metabolic engineering that would increase rutin content in cultivars of common buckwheat.
Highlights
Buckwheat is a minor crop that belongs to the eudicot family Polygonaceae, genus Fagopyrum
We found 1928 unigenes were categorized as posttranslational modifications, protein turnover, and chaperones, which illustrates active biosynthesis during seed development; 1301 unigenes were involved in signal transduction mechanism; 1104 unigenes were related to translation, ribosomal structure, and biogenesis; 897 unigenes were associated with intracellular trafficking, secretion, and vesicular transport; 862 unigenes were implicated in transcription;844 unigenes were involved in secondary metabolite biosynthesis, transport, and catabolism; 807 unigenes were related to carbohydrate transport and metabolism
Enrichment analysis showed that the transcription levels of enzymes in the flavonoid biosynthesis pathway correlated with higher rutin content in developing Fea seeds compared to F. esculentum (Fes)
Summary
Buckwheat is a minor crop that belongs to the eudicot family Polygonaceae, genus Fagopyrum. Buckwheat is well known for its pharmaceutical potential to protect people from cardiovascular disease, diabetes, and cancers, which is predominantly attributed to its content of rutin, quercetin and other flavonols with antioxidant and anti-inflammatory bioactivities [2]. These characteristics have made this plant more popular as a healthy, yet traditional food crop, and demand for buckwheat products grows each year. Fes is selfincompatible with an dulled seed coat, whereas Ft is self-compatible with a tight seed coat These species differ in their morphology, flour flavor, and seed rutin content [7,8,9]. Studies focused on the starch and sucrose metabolism regulation of buckwheat species are still missed[14]
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