B-Box Transcription Factor FaBBX22 Promotes Light-Induced Anthocyanin Accumulation in Strawberry (Fragaria × ananassa)

Abstract

B-box transcription factors (TFs) play a vital role in light-induced anthocyanin accumulation. Here, the FaBBX22 gene encoding 287 amino acids B-box TF was isolated from the cultivated strawberry variety ‘Benihoppe’ and characterized functionally. The expression analysis showed that FaBBX22 was expressed in the roots, stems, leaves, flowers and fruits, and its transcription level was upregulated under the red- or blue-light irradiation. FaBBX22 was localized in the nucleus and showed trans-acting activity in yeast cells. Ectopic overexpression of FaBBX22 in Arabidopsis enhanced the accumulation of anthocyanin. Additionally, we obtained transgenic strawberry calli that overexpressed the FaBBX22 gene, and strawberry calli coloration assays showed that FaBBX22 increased anthocyanin accumulation by upregulating the expression of anthocyanin biosynthetic genes (FaPAL, FaANS, FaF3′H, FaUFGT1) and transport gene FaRAP in a light-dependent manner. Yeast two-hybrid (Y2H) and bimolecular fluorescence complementation assays indicated that FaBBX22 interacted with FaHY5. Furthermore, mutation of the 70th Asp residue in FaBBX22 protein to an Ala residue disrupted the interaction between FaBBX22 and FaHY5. Further, a transient expression assay demonstrated that the co-expression of FaBBX22 and FaHY5 could strongly promote anthocyanin accumulation in strawberry fruits. Collectively, these results revealed the positive regulatory role of FaBBX22 in light-induced anthocyanin accumulation.

A novel R2R3‐MYB transcription factor FaMYB5 positively regulates anthocyanin and proanthocyanidin biosynthesis in cultivated strawberries (Fragaria × ananassa)

“…For transgenic strawberry calli, 3 × FLAG‐FaMYB5‐3 × FLAG and 6 × HIS‐FaBT2‐6 × HIS were cloned into a pCAMBIA‐35SN vector and transformed into Agrobacterium GV3101. Then, the transgenic strawberry calli were generated by the Agrobacterium‐mediated leaf disk transformation method, as we described previously (Liu et al ., 2022a). For the induction of flavonoid synthesis, the calli were first cultured in dark for 2 weeks and then transferred to a hormone‐free MS medium and continuously treated under light for 96 h.…”

Genome-Wide Identification of Strawberry C2H2-ZFP C1-2i Subclass and the Potential Function of FaZAT10 in Abiotic Stress

“…In addition, the result indicates that the yeast strains that transformed with pGBKT7-FaZAT10 (validation group) and pGBKT7-Lam (a negative control) could not grow normally on SD/-Trp/-His/-Ade/X-α-gal and SD/-Trp/-His/-Ade media. The positive group pGBKT7-FaBBX22 [ 31 ] grew well on SD/-Trp/-His/-Ade/X-α-gal medium and turned blue, which indicates that FaZAT10 has no trans-acting ability in yeast cells ( Figure 9 B).…”

“…The full-length CDS of FaZAT10 was inserted into the yeast expression vector pGBKT7 (BD) using the homologous recombination method. After confirming the positive vector, the transcriptional activity of the FaZAT10 protein was detected by transforming pGBKT7-Lam (a negative control), pGBKT7-FaBBX22 (a positive control) [ 31 ], and pGBKT7-FaZAT10 (validation group) into Y2H cold. After three days of culture at 28 °C, the growth of the yeast strains on different defective media (SD/ −Trp and SD/ −Trp-Ade-His /X-α-gal) was observed.…”

Insights into transcription factors controlling strawberry fruit development and ripening

“…Thus, both TFs are induced by light in strawberries ( Xu et al., 2018 ) and their transient overexpression promote anthocyanin biosynthesis, interacting to form an heterodimeric complex that directly binds to the promoters of CHS and DFR ( Li et al., 2020 ). In a similar way, the B-Box TF FaBBX22 is able to form heterodimers with FaHY5 and regulate PAL , ANS , F3’H , UFGT and RAP gene expression in a light-dependent manner, resulting in a higher accumulation of anthocyanins ( Liu et al., 2022 ).…”