Overexpression ofPtrMYB119, a R2R3-MYB transcription factor fromPopulus trichocarpa, promotes anthocyanin production in hybrid poplar

Abstract

Anthocyanins are a group of colorful and bioactive natural pigments with important physiological and ecological functions in plants. We found an MYB transcription factor (PtrMYB119) from Populus trichocarpa that positively regulates anthocyanin production when expressed under the control of the CaMV 35S promoter in transgenic Arabidopsis Amino acid sequence analysis revealed that PtrMYB119 is highly homologous to Arabidopsis PAP1 (PRODUCTION OF ANTHOCYANIN PIGMENT1), a well-known transcriptional activator of anthocyanin biosynthesis. Independently produced transgenic poplars overexpressing PtrMYB119 or PtrMYB120 (a paralogous gene to PtrMYB119) (i.e., 35S::PtrMYB119 and 35S::PtrMYB120, respectively) showed elevated accumulation of anthocyanins in the whole plants, including leaf, stem and even root tissues. Using a reverse-phase high-performance liquid chromatography, we confirmed that the majority of the accumulated anthocyanin in our transgenic poplar is cyanidin-3-O-glucoside. Gene expression analyses revealed that most of the genes involved in the anthocyanin biosynthetic pathway were highly upregulated in 35S::PtrMYB119 poplars compared with the nontransformed control poplar. Among these genes, expression of PtrCHS1 (Chalcone Synthase1) and PtrANS2 (Anthocyanin Synthase2), which catalyze the initial and last steps of anthocyanin biosynthesis, respectively, was upregulated by up to 350-fold. Subsequent transient activation assays confirmed that PtrMYB119 activated the transcription of both PtrCHS1 and PtrANS2 Interestingly, expression of MYB182, a repressor of both anthocyanin and proanthocyanidin (PA) biosynthesis, was largely suppressed in 35S::PtrMYB119 poplars, while expression of MYB134, an activator of PA biosynthesis, was not changed significantly. More interestingly, high-level accumulation of anthocyanins in 35S::PtrMYB119 poplars did not have an adverse effect on plant growth. Taken together, our results demonstrate that PtrMYB119 and PtrMYB120 function as transcriptional activators of anthocyanin accumulation in both Arabidopsis and poplar.

R2R3‐MYB transcription factor MYB6 promotes anthocyanin and proanthocyanidin biosynthesis but inhibits secondary cell wall formation in Populus tomentosa

“…In the poplar genome, 192 R2R3 MYB transcription factors have been predicted (Wilkins et al ., ), but only a small number of MYB members, including MYB134 (Mellway et al ., ), MYB182 (Yoshida et al ., ), MYB119 (Cho et al ., ), MYB57 (Wan et al ., ), MYB115 (James et al ., ; Wang et al ., ), PtrMYB012 (Kim et al ., ), and MYB165 and MYB192 (Ma et al ., ), have been found to regulate the flavonoid biosynthetic pathway. In the study reported herein, we isolated and characterized the poplar transcription factor MYB6, which shows high homology in amino acid sequences to other MYB5‐like transcription factors.…”

Genome sequence and genetic transformation of a widely distributed and cultivated poplar

“…A genetic transformation system for P. trichocarpa was established just after its genome had been reported (Song et al, 2006), it is still difficult to transform and grow this species in some labs or regions of the North Hemisphere. In numerous molecular studies on poplar have therefore used the P. trichocarpa genome for gene sequence and expression analyses, but for physiological and phenotypic tests other hybrid poplars have been transformed, for example, P. tremula 9 tremuloides (Ohtani et al, 2011), P. alba 9 grandidentata (Maloney and Mansfield, 2010), P. alba 9 P. tremula (Cho et al, 2016) and P. simonii 9 P. nigra (Zhao et al, 2017). Attributed to the different genetic backgrounds and gene sequences and/or variations in copy number of homologs between different species, such heterogeneous transformation (Han et al, 1997(Han et al, , 2000Ma et al, 2004) may give rise to numerous unexpected results in phenotypic and molecular analyses.…”

Two R2R3‐MYB proteins are broad repressors of flavonoid and phenylpropanoid metabolism in poplar

“…These transcription factors physically interact with poplar bHLH131, and their overexpression transgenic poplar leads to hyperaccumulation of PAs (Mellway et al, 2009;James et al, 2017). Anthocyanin accumulation in poplar is controlled by two PAP1-like activators, MYB117 and MYB119 (Yoshida et al, 2015;Cho et al, 2016). As in grapevine, the poplar genome also contains an expanded suite of flavonoid MYB repressors.…”