Tartary buckwheat (Fagopyrum tataricum Gaertn.) is a coarse cereal with strongly abiotic resistance. The MYB family plays a regulatory role in plant growth, development, and responses to biotic and abiotic stresses. However, the characteristics and regulatory mechanisms of MYB transcription factors in Tartary buckwheat remain unclarified. Here, this study cloned the FtMYB22 gene from Tartary buckwheat, and investigated its involvement in responding to individual water deficit and salt stress in Arabidopsis. Sequence analysis highlighted that the N-termini of FtMYB22 contained two highly conserved SANT domains and one conserved domain from the SG20 subfamily. Nucleus-localized FtMYB22 did not have individual transcriptional activation activity. Water deficiency and salt stress induced the high expression of the GUS gene, which was driven by the promoter of FtMYB22. Yeast stress experiments showed that the overexpression of FtMYB22 significantly reduced the growth activity of transgenic yeast under water deficit or salt stress. Consistently, the overexpression of FtMYB22 reduced the salt and water deficit stress resistance of the transgenic plants. In addition, physiological parameters showed that transgenic plants had lower proline and antioxidant enzyme activity under stress conditions. Compared to the wild-type (WT), transgenic plants accumulated more malondialdehyde (MDA), H₂O₂, and O₂⁻; they also showed higher ion permeability and water loss rates of detached leaves under stress treatments. Notably, FtMYB22 was involved in plant stress resistance through an ABA-dependent pathway. Under stress conditions, the expression of RD29A, RD29B, PP2CA, KIN1, COR15A, and other genes in response to plant stress in transgenic lines was significantly lower than that in the WT (p < 0.05). Furthermore, yeast two-hybrid assay showed that there was a significant interaction between FtMYB22 and the ABA receptor protein RCAR1/2, which functioned in the ABA signal pathway. Altogether, FtMYB22, as a negative regulator, inhibited a variety of physiological and biochemical reactions, affected gene expression and stomatal closure in transgenic plants through the ABA-dependent pathway, and reduced the tolerance of transgenic Arabidopsis to water deficiency and salt stress. Based on these fundamental verifications, further studies would shed light on the hormone signal response mechanism of FtMYB22.

Anthocyanin is one important nutrition composition in Tartary buckwheat (Fagopyrum tataricum) sprouts, a component missing in its seeds. Although anthocyanin biosynthesis requires light, the mechanism of light-induced anthocyanin accumulation in Tartary buckwheat is unclear. Here, comparative transcriptome analysis of Tartary buckwheat sprouts under light and dark treatments and biochemical approaches were performed to identify the roles of one B-box protein BBX22 and ELONGATED HYPOCOTYL 5 (HY5). The overexpression assay showed that FtHY5 and FtBBX22 could both promote anthocyanin synthesis in red-flower tobacco. Additionally, FtBBX22 associated with FtHY5 to form a complex that activates the transcription of MYB transcription factor genes FtMYB42 and FtDFR, leading to anthocyanin accumulation. These findings revealed the regulation mechanism of light-induced anthocyanin synthesis and provide excellent gene resources for breeding high-quality Tartary buckwheat.

Tartary buckwheat (Fagopyrum tataricum Gaertn.) belongs to the family of Polygonaceae and is used as a multi-functional plant. R2R3-MYB transcription factors play a crucial part in plant growth and are involved in many biological processes where they regulate their internal environment. To date, there is no documented systematic research on the R2R3-MYB gene family in Tartary buckwheat. Here, domain features, chromosomal location, motif prediction, gene structure, cis-acting elements, as well as the expression pattern of R2R3-MYB transcription factors were analyzed comprehensively in Tartary buckwheat using a bioinformatic approach. Additionally, one R2R3-MYB gene was verified by transgenic Arabidopsis. Results indicate that a total of 152 R2R3-MYB genes were identified with special R2R3 domains and were distributed on 8 chromosomes of Tartary buckwheat. They were further classified into 25 sub-categories via phylogenetic analysis in terms of the R2R3-MYB gene family classification principles of Arabidopsis thaliana. This classification was further supported by analysis of exon–intron structure, motif, and cis-elements. Tandem and segmental duplication existed among the R2R3-MYB gene family of Tartary buckwheat, and there were 5, 8, 27, and 36 FtR2R3-MYB homologous genes, respectively, when comparing with Zea mays, Oryza sativa, Arabidopsis thaliana, and Solanum melongena by synteny analysis. The expression pattern of FtR2R3-MYB genes in different tissue and under salt stress and different light condition showed that members had tissue-specific expression levels and that these members may play diverse functions in plant growth and adaptation to varying environments. In addition, one of the FtR2R3-MYB gene families, FtMYB43, a homologue of AtTT2, clustered with R2R3-MYB from other plant species, which were reported to be involved in the regulation of anthocyanin or proanthocyanidin biosynthesis. This gene was located in the nucleus, and had transcriptional activation activity, indicating that FtMYB43 may be a positive transcript factor of anthocyanin or proanthocyadin biosynthesis. Moreover, the function of FtMYB43 was further verified to improve the production of anthocyanin in transgenic Arabidopsis by overexpression, and qRT-PCR assay implied that FtMYB43 may regulate the expression levels of most structural genes of the anthocyanin biosynthesis pathway in Arabidopsis seedlings. These results provide more insights into the structure and function of the R2R3-MYB gene family and may accelerate the breeding of ornamental buckwheat cultivars.