Abstract
Main ConclusionGbMYBR1, a new type of R2R3-MYB repressor from Ginkgo biloba, displayed pleiotropic effects on plant growth, phenylpropanoid accumulation, by regulating multiple related genes at different levels.Ginkgo biloba is a typical gymnosperm that has been thriving on earth for millions of years. MYB transcription factors (TFs) play important roles in diverse processes in plants. However, the role of MYBs remains largely unknown in Ginkgo. Here, an MYB TF gene from Ginkgo, designated as GbMYBR1, was found to act as a repressor in multiple processes. GbMYBR1 was mainly expressed in the leaves of Ginkgo. Over-expression of GbMYBR1 in Arabidopsis thaliana led to growth retardation, decreases in lignin content, reduced trichome density, and remarkable reduction in anthocyanin and flavonol contents in leaves. Proanthocyanidin content was decreased in the seeds of transgenic Arabidopsis, which led to light-brown seed color. Both qPCR and transcriptome sequencing analyses demonstrated that the transcript levels of multiple genes related to phenylpropanoid biosynthesis, trichome formation, and pathogen resistance were down-regulated in the transgenic Arabidopsis. In particular, we found that GbMYBR1 directly interacts with the bHLH cofactor GL3 as revealed by yeast two-hybrid assays. Our work indicated that GbMYBR1 has pleiotropic effects on plant growth, phenylpropanoid accumulation, and trichome development, mediated by interaction with GL3 or direct suppression of key pathway genes. Thus, GbMYBR1 represents a novel type of R2R3 MYB repressor.
Highlights
The MYB transcription factors (TFs) comprise one of the largest families of transcriptional regulators in plants
The deduced GbMYBR1 protein showed less than 25% identity to Ginkgo MYBF2 that was reported to suppress flavonol and anthocyanin biosynthesis in Arabidopsis (Xu et al 2014a)
The biosynthesis of phenylpropanoids is subject to sophisticated regulation by different types of TFs (Broun 2005)
Summary
The MYB transcription factors (TFs) comprise one of the largest families of transcriptional regulators in plants. They are involved in diverse processes, including development, stress responses, and metabolism (Ramsay and Glover 2005; Liu et al 2015a; Roy 2016). These processes, including flavonoid biosynthesis, trichome initiation, mucilage production, and root hair initiation, are linked and regulated by a same set of TF complex. In the model plant Arabidopsis, the ternary MBW (MYBbHLH-WDR) complexes, which are composed of R2R3MYB, bHLH (basic helix-loop-helix), and WD40 repeat (WDR) proteins, regulate the biosynthesis of flavonoids (e.g., anthocyanins and proanthocyanidins; Lepiniec et al 2006; Li 2014). TTG1 and TT8 can interact with the R2R3-MYB-type TF TT2 to regulate proanthocyanidin accumulation in seeds (Gonzalez et al 2009)
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