Isolation of cDNAs for R2R3-MYB, bHLH and WDR Transcriptional Regulators and Identification of c and ca Mutations Conferring White Flowers in the Japanese Morning Glory

Abstract

The transcriptional regulators for anthocyanin biosynthesis include members of proteins containing an R2R3-MYB domain, a bHLH (basic helix-loop-helix) domain and conserved WD40 repeats (WDRs). Spacial and temporal expression of the structural genes encoding the enzymes for anthocyanin biosynthesis is thought to be determined by combinations of the R2R3-MYB, bHLH and WDR factors and their interactions. While the wild-type Japanese morning glory (Ipomoea nil) exhibits blue flowers with colored stems and dark-brown seeds, the c mutants display white flowers with red stems and colored seeds, and the ca mutants exhibit white flowers with green stems and ivory seeds. Here, we characterize the tissue-specific expression of three MYB genes, three bHLH genes and two WDR genes in I. nil. We also show that the recessive c-1 and ca alleles are frameshift mutations caused by a 2 bp deletion and 7 bp insertions in the genes for the R2R3-MYB and WDR transcriptional regulators designated as InMYB1 and InWDR1, respectively. In addition to defects in flower, stem and seed pigmentations, the ca mutants were found to show reduced trichome formation in seeds but to produce leaf and stem trichomes and root hairs normally. Except for the gene for chalcone synthase E in the ca mutant, all structural genes tested were coordinately reduced in both c-1 and ca mutant flower limbs. However, slight but significant expression of the genes for chalcone synthase D, chalcone isomerase and flavanone 3-hydroxylase in the pathway for flavonol biosynthesis was detectable in c-1 and ca mutants, whereas no such residual expression could be observed in other genes involved in the later anthocyanin biosynthesis pathway. The biological roles of the C-1 and Ca genes in I. nil epidermal traits and their evolutionary implications are also discussed.

MYB transcription factor genes as regulators for plant responses: an overview

“…In Antirrhinum majus and tobacco, AmMYB305 (or its orthologue in tobacco) activated the gene encoding the first enzyme of phenylpropanoid metabolism, phenylalanine ammonia lyase (PAL) (Urao et al 1993). Morita et al (2006) reported that spatial and temporal expression of the structural genes encoding the enzymes for anthocyanin biosynthesis was determined by combinations of the R2R3-MYB, bHLH and WDR factors and their interaction. Lin- Wang et al (2010) described the association of MYBA or MYB1 and MYB10 with regulation of the anthocyanin biosynthetic pathway in Rosaceae.…”

The Methylation of the PcMYB10 Promoter Is Associated with Green-Skinned Sport in Max Red Bartlett Pear

“…For example, mutations in the structural genes CHS (for chalcone synthase), DFR (for dihydroflavonol 4-reductase), and ANS (for anthocyanidin synthase) involved in anthocyanin biosynthesis cause flower color changes (Stracke et al, 2009;Tanaka et al, 2009;Vanholme et al, 2010). Genetic mutations causing color changes of plant organs also occur in genes regulating anthocyanin biosynthesis, such as transcription factors (Boss et al, 1996;Morita et al, 2006;Park et al, 2007;Allan et al, 2008;Chiu et al, 2010). The transcription factors involved in anthocyanin biosynthesis include R2R3-MYB, bHLH (for basic helix-loop-helix), and WDR (for WD-repeat protein), which regulate the downstream structural genes by forming the MYBbHLH-WD40 complex, which is involved in the anthocyanin biosynthesis pathway (Holton and Cornish, 1995;Winkel-Shirley, 2001;Schwinn et al, 2006;Gonzalez et al, 2008).…”

“…The transcription factors involved in anthocyanin biosynthesis include R2R3-MYB, bHLH (for basic helix-loop-helix), and WDR (for WD-repeat protein), which regulate the downstream structural genes by forming the MYBbHLH-WD40 complex, which is involved in the anthocyanin biosynthesis pathway (Holton and Cornish, 1995;Winkel-Shirley, 2001;Schwinn et al, 2006;Gonzalez et al, 2008). Mutations including nucleotide substitutions, deletions, and insertions in the MYB gene result in color changes in plant organs (Boss et al, 1996;Morita et al, 2006). Transposon insertions in the bHLH gene cause white flowers in common morning glory (Ipomoea purpurea; Park et al, 2007), whereas simultaneous mutations of a nucleotide deletion in MYB and a nucleotide insertion in WDR change morning glory flower color from blue to white (Chiu et al, 2010).…”

Transcriptional regulators of flavonoid biosynthesis and their application to flower color modification in Japanese gentians

“…Regulatory genes have been also characterized in several ornamental plant species, including Japanese morning glory (Morita et al 2006), gerbera (Elomaa et al 1998;Elomaa et al 2003), torenia (Nishijima et al 2013), Mimulus aurantiacus (Streisfeld et al 2013), and peach (Uematsu et al 2014). Several reports have appeared on the regulation of floral anthocyanin pigmentation in non-ornamental plants, such as soybean (Takahashi et al 2013), kiwifruit (Fraser et al 2013), and tobacco (Pattanaik et al 2010).…”