The appropriate specification and patterning of distinct cell types is essential for the proper development of multicellular organisms. The developmental pathways for trichomes and root hairs in Arabidopsis have proven useful as models for studying cell fate determination in plant. The current picture is that R2R3MYB transcription factor GLABROUS1 (GL1), the bHLH transcription factors ENHANCER OF GLABRA 1 and ENHANCER OF GLABRA 3 (EGL1and EGL3) and the WD40 repeat protein Transparent Testa Glabra 1 (TTG1) form the MBW (MYBbHLH-WDR) ternary transcriptional complex that promotes trichome development. The activity of this complex is counteracted by single R3 repeat MYBs through competition for binding of the R2R3MYB factors to the bHLH protein. The R3MYB protein TRIPTYCHON (TRY) was originally identified as a negative regulator of trichome initiation in Arabidopsis, working within the MBW complex specifying epidermal patterning mechanisms (Schellmann et al. EMBO J. 2002). The MBW complex has multifold activities in Arabidopsis where it also controls mucilage production, anthocyanin and proanthocyanindin (PA) biosynthesis. To assay for TRY activity within the different MBW complexes in Arabidopsis and test whether TRY is a useful tool to identify MBW complex activity in other plant species, we overexpressed this transcription factor in Arabidopsis and tobacco. Here we show that TRY overexpression in Arabidopsis interferes with not only the MBW complexes promoting trichome and root hair development, but also with the ternary complex that controls anthocyanin accumulation in vegetative tissues. Under anthocyanin inducing conditions, TRY transgenic plants showed a marked reduction in pigmentation due to transcriptional repression of both early and late biosynthetic genes of the flavonoid pathway as well as of TT8, the bHLH partner in the anthocyanin MBW complex. Furthermore, Arabidopsis lines with highest transgene steady state mRNA levels also displayed reduced seed coat PA accumulation. While the effect of TRY on the MBW complex regulating anthocyanin production appears to be less penetrating than its effect on trichomes/root hairs in Arabidopsis, in tobacco TRY affected neither trichome nor root hair specification, but did significantly reduce floral pigmentation. As such TRY repressed, in a dose-dependent manner, the transcription of DFR and ANS, the two key biosynthetic genes of the anthocyanin pathway, to produce tobacco transgenic lines exhibiting pale pink to white flowers. In conclusion, the present study lends support to the thesis that in the Asterid division, the Eudicot clade to which tobacco belongs, the proteins guiding the formation of trichomes likely have a distinct evolutionary origin (Serna and Martin, Trends Plant Science 2006).
The R3MYB AtTRY gene interferes with genes of the MBW complex that controls flavonoid biosynthesis
Paolocci F;
2009
Abstract
The appropriate specification and patterning of distinct cell types is essential for the proper development of multicellular organisms. The developmental pathways for trichomes and root hairs in Arabidopsis have proven useful as models for studying cell fate determination in plant. The current picture is that R2R3MYB transcription factor GLABROUS1 (GL1), the bHLH transcription factors ENHANCER OF GLABRA 1 and ENHANCER OF GLABRA 3 (EGL1and EGL3) and the WD40 repeat protein Transparent Testa Glabra 1 (TTG1) form the MBW (MYBbHLH-WDR) ternary transcriptional complex that promotes trichome development. The activity of this complex is counteracted by single R3 repeat MYBs through competition for binding of the R2R3MYB factors to the bHLH protein. The R3MYB protein TRIPTYCHON (TRY) was originally identified as a negative regulator of trichome initiation in Arabidopsis, working within the MBW complex specifying epidermal patterning mechanisms (Schellmann et al. EMBO J. 2002). The MBW complex has multifold activities in Arabidopsis where it also controls mucilage production, anthocyanin and proanthocyanindin (PA) biosynthesis. To assay for TRY activity within the different MBW complexes in Arabidopsis and test whether TRY is a useful tool to identify MBW complex activity in other plant species, we overexpressed this transcription factor in Arabidopsis and tobacco. Here we show that TRY overexpression in Arabidopsis interferes with not only the MBW complexes promoting trichome and root hair development, but also with the ternary complex that controls anthocyanin accumulation in vegetative tissues. Under anthocyanin inducing conditions, TRY transgenic plants showed a marked reduction in pigmentation due to transcriptional repression of both early and late biosynthetic genes of the flavonoid pathway as well as of TT8, the bHLH partner in the anthocyanin MBW complex. Furthermore, Arabidopsis lines with highest transgene steady state mRNA levels also displayed reduced seed coat PA accumulation. While the effect of TRY on the MBW complex regulating anthocyanin production appears to be less penetrating than its effect on trichomes/root hairs in Arabidopsis, in tobacco TRY affected neither trichome nor root hair specification, but did significantly reduce floral pigmentation. As such TRY repressed, in a dose-dependent manner, the transcription of DFR and ANS, the two key biosynthetic genes of the anthocyanin pathway, to produce tobacco transgenic lines exhibiting pale pink to white flowers. In conclusion, the present study lends support to the thesis that in the Asterid division, the Eudicot clade to which tobacco belongs, the proteins guiding the formation of trichomes likely have a distinct evolutionary origin (Serna and Martin, Trends Plant Science 2006).I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
