Hybridization with Fagopyrum cymosum Meisn. as a way to make cultivated Tartary buckwheat (F. tataricum Gaertn.) with grain characteristics typical for common buckwheat (F. esculentum Moench.).

Compared to common buckwheat (F. esculentum), Tartary buckwheat (F. tataricum) is very polymorphic in the type of seeds, but a seed type which is typical for F. esculentum, i.e. triangular seeds with flat sides and clear ribs, has been not found among the polymorphism. However, such seed type is typical for wild species F. cymosum which produces fertile hybrids in crosses with F. tataricum. Embryo rescue based interspecific cross F. esculentum × F. cymosum allowed reveal functional allelism of the genes determining the similar morphs of these species' seeds, i.e. the seed type resulted from mutation(s) at same gene. The gene can be assigned as TAN (triangular). Variation for the seed shell thickness among recessives for the TAN carrying about 12% of F. tataricum genome, together with the shell thickness of a seed from the F1 hybrid F. esculentum × F. cymosum compared to ones of the parents, suggests there are some genes influencing seed shell thickness. Also, it was supported by analyses of seeds characteristics of Tartary-based forms with some share of F. cymosum genetic material. In addition, cross F. tataricum × F. cymosum looks like an effective tool to increase 1000-seed weight of Tartary buckwheat-based breeding material.

Reproductive development of common buckwheat (Fagopyrum esculentum Moench) and its wild relatives provides insights into their evolutionary biology.

Introduction: Understanding the complex inflorescence architecture and developmental morphology of common buckwheat (Fagopyrum esculentum) is crucial for crop yield. However, most published descriptions of early flower and inflorescence development in Polygonaceae are based on light microscopy and often documented by line drawings. In Fagopyrum and many other Polygonaceae, an important inflorescence module is the thyrse, in which the primary axis never terminates in a flower and lateral cymes (monochasia) produce successively developing flowers of several orders. Each flower of a cyme is enclosed together with the next-order flower by a bilobed sheathing bract-like structure of controversial morphological nature. Methods: We explored patterns of flower structure and arrangement in buckwheat and its wild relatives, using comparative morphology, scanning electron microscopy and X-ray microtomography. Results: Our data support interpretation of the sheathing bract as two congenitally fused phyllomes (prophylls), one of which subtends a next-order flower. In tepal-like bract, a homeotic mutant of F. esculentum, the bilobed sheathing bract-like organ acquires tepal-like features and is sometimes replaced by two distinct phyllomes. Wild representatives of F. esculentum (ssp. ancestrale) and most cultivars of common buckwheat possess an indeterminate growth type with lateral thyrses produced successively on the primary inflorescence axis until cessation of growth. In contrast, determinate cultivars of F. esculentum develop a terminal thyrse after producing lateral thyrses. In contrast to F. esculentum, the occurrence of a terminal thyrse does not guarantee a determinate growth pattern in F. tataricum. The number of lateral thyrses produced before the terminal thyrse on the main axis of F. tataricum varies from zero to c. 19. Discussion: The nine stages of early flower development formally recognized here and our outline of basic terminology will facilitate more standardized and readily comparable descriptions in subsequent research on buckwheat biology. Non-trivial relative arrangements of tepals and bracteoles in Fagopyrum and some other Polygonaceae require investigation using refined approaches to mathematical modelling of flower development. Our data on inflorescence morphology and development suggest contrasting evolutionary patterns in the two main cultivated species of buckwheat, F. esculentum and F. tataricum. The genus Fagopyrum offers an excellent opportunity for evo-devo studies related to inflorescence architecture.

High-Resolution Transcriptome Atlas and Improved Genome Assembly of Common Buckwheat, Fagopyrum esculentum.

Common buckwheat (Fagopyrum esculentum) is an important non-cereal grain crop and a prospective component of functional food. Despite this, the genomic resources for this species and for the whole family Polygonaceae, to which it belongs, are scarce. Here, we report the assembly of the buckwheat genome using long-read technology and a high-resolution expression atlas including 46 organs and developmental stages. We found that the buckwheat genome has an extremely high content of transposable elements, including several classes of recently (0.5-1 Mya) multiplied TEs ("transposon burst") and gradually accumulated TEs. The difference in TE content is a major factor contributing to the three-fold increase in the genome size of F. esculentum compared with its sister species F. tataricum. Moreover, we detected the differences in TE content between the wild ancestral subspecies F. esculentum ssp. ancestrale and buckwheat cultivars, suggesting that TE activity accompanied buckwheat domestication. Expression profiling allowed us to test a hypothesis about the genetic control of petaloidy of tepals in buckwheat. We showed that it is not mediated by B-class gene activity, in contrast to the prediction from the ABC model. Based on a survey of expression profiles and phylogenetic analysis, we identified the MYB family transcription factor gene tr_18111 as a potential candidate for the determination of conical cells in buckwheat petaloid tepals. The information on expression patterns has been integrated into the publicly available database TraVA: http://travadb.org/browse/Species=Fesc/. The improved genome assembly and transcriptomic resources will enable research on buckwheat, including practical applications.

Mitochondrial Genome of Fagopyrum esculentum and the Genetic Diversity of Extranuclear Genomes in Buckwheat.

Fagopyrum esculentum (common buckwheat) is an important agricultural non-cereal grain plant. Despite extensive genetic studies, the information on its mitochondrial genome is still lacking. Using long reads generated by single-molecule real-time technology coupled with circular consensus sequencing (CCS) protocol, we assembled the buckwheat mitochondrial genome and detected that its prevalent form consists of 10 circular chromosomes with a total length of 404 Kb. In order to confirm the presence of a multipartite structure, we developed a new targeted assembly tool capable of processing long reads. The mitogenome contains all genes typical for plant mitochondrial genomes and long inserts of plastid origin (~6.4% of the total mitogenome length). Using this new information, we characterized the genetic diversity of mitochondrial and plastid genomes in 11 buckwheat cultivars compared with the ancestral subspecies, F. esculentum ssp. ancestrale. We found it to be surprisingly low within cultivars: Only three to six variations in the mitogenome and one to two in the plastid genome. In contrast, the divergence with F. esculentum ssp. ancestrale is much higher: 220 positions differ in the mitochondrial genome and 159 in the plastid genome. The SNPs in the plastid genome are enriched in non-synonymous substitutions, in particular in the genes involved in photosynthesis: psbA, psbC, and psbH. This presumably reflects the selection for the increased photosynthesis efficiency as a part of the buckwheat breeding program.