Abstract
Extensive studies have shown that the MBW complex consisting of three kinds of regulatory proteins, MYB and basic helix–loop–helix (bHLH) transcription factors and a WD40 repeat protein, TRANSPARENT TESTA GLABRA1 (TTG1), acts in concert to promote trichome formation and flavonoid accumulation in Arabidopsis thaliana. TTG1 functions as an essential activator in these two biological processes. However, direct downstream targets of the TTG1-dependent MBW complex have not yet been obtained in the two biological processes at the genome-wide level in A. thaliana. In the present study, we found, through RNA sequencing and quantitative real-time PCR analysis, that a great number of regulatory and structural genes involved in both trichome formation and flavonoid accumulation are significantly downregulated in the young shoots and expanding true leaves of ttg1-13 plants. Post-translational activation of a TTG1-glucocorticoid receptor fusion protein and chromatin immunoprecipitation assays demonstrated that these downregulated genes are directly or indirectly targeted by the TTG1-dependent MBW complex in vivo during trichome formation and flavonoid accumulation. These findings further extend our understanding of the role of TTG1-dependent MBW complex in the regulation of trichome formation and flavonoid accumulation in A. thaliana.
Highlights
TRANSPARENT TESTA GLABRA1 (TTG1) encodes a WD40 repeat transcription factor that plays pleiotropic roles in the regulation of seed development and postembryonic processes in Arabidopsis thaliana [1,2,3,4,5,6,7,8]
We found that there were 4 downregulated regulatory genes involved in both trichome formation and flavonoid biosynthesis, TESTA GLABRA2 (TTG2), TT8, GL2, and MYC2 (Figures 1 and 2; Tables 1 and 2), among which the former two genes and the latter two genes were directly and indirectly regulated by the TTG1-dependent MYB–basic helix–loop–helix (bHLH)–WD40 (MBW) complex (Figures 3 and 4, and Figure S3), in the ttg1-13 young shoots and expanding true leaves
It can be deduced that the TTG1-dependent MBW complex promotes TT8 expression probably independent of GL2, or the simulative effect of the TTG1-dependent MBW complex and/or other downregulated regulatory genes is stronger than the inhibitory effect of GL2 on the TT8 expression, in the young shoots and expanding true leaves
Summary
TRANSPARENT TESTA GLABRA1 (TTG1) encodes a WD40 repeat transcription factor that plays pleiotropic roles in the regulation of seed development and postembryonic processes in Arabidopsis thaliana [1,2,3,4,5,6,7,8]. During seed development, it promotes the biosynthesis of proanthocyanidins (PAs) [1,2,3,8,9] and accelerates the production of mucilage and columella [1,8,10,11]. The further study indicated that TTG1 represses the activation of the CAPRICE (CPC) promoter by GL1 and GL3, and GL1 suppresses the activation of the TRIPTYCHON promoter by GL3 and TTG1 [26]
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