Genetic analysis of the liverwort Marchantia polymorpha reveals that R2R3MYB activation of flavonoid production in response to abiotic stress is an ancient character in land plants

Abstract

The flavonoid pathway is hypothesized to have evolved during land colonization by plants c. 450 Myr ago for protection against abiotic stresses. In angiosperms, R2R3MYB transcription factors are key for environmental regulation of flavonoid production. However, angiosperm R2R3MYB gene families are larger than those of basal plants, and it is not known whether the regulatory system is conserved across land plants. We examined whether R2R3MYBs regulate the flavonoid pathway in liverworts, one of the earliest diverging land plant lineages. We characterized MpMyb14 from the liverwort Marchantia polymorpha using genetic mutagenesis, transgenic overexpression, gene promoter analysis, and transcriptomic and chemical analysis. MpMyb14 is phylogenetically basal to characterized angiosperm R2R3MYB flavonoid regulators. Mpmyb14 knockout lines lost all red pigmentation from the flavonoid riccionidin A, whereas overexpression conferred production of large amounts of flavones and riccionidin A, activation of associated biosynthetic genes, and constitutive red pigmentation. MpMyb14 expression and flavonoid pigmentation were induced by light- and nutrient-deprivation stress in M. polymorpha as for anthocyanins in angiosperms. MpMyb14 regulates stress-induced flavonoid production in M. polymorpha, and is essential for red pigmentation. This suggests that R2R3MYB regulated flavonoid production is a conserved character across land plants which arose early during land colonization.

UVR8‐mediated induction of flavonoid biosynthesis for UVB tolerance is conserved between the liverwort Marchantia polymorpha and flowering plants

“…Amongst other transcription factors induced strongly were MYB14 ( Mapoly0073s0038 ), MYB6 ( Mapoly0019s0071 ) and bHLH4 ( Mapoly0028s0058 ). MYB14 activates flavonoid biosynthesis (Albert et al ., ). The function of MYB6 or bHLH4 is unknown; however, the top Arabidopsis BLAST hits for Mp bHLH4 were At MYC4 and At TT8 , which are regulators of jasmonic acid responses (Fernández‐Calvo et al ., ) and the flavonoid biosynthetic pathway, respectively.…”

“…The function of CHIL is uncertain, but inhibition of CHIL production in angiosperms reduces flavonoid production (Morita et al ., ; Jiang et al ., ). Additionally, previously generated mutant and overexpression transgenics for Mp MYB14 (Albert et al ., ) were included in the analyses.…”

“…Although the HY5 signal pathway was important for induction of flavone biosynthesis, marchantia may not have a downstream target R2R3MYB transcription factor equivalent to the SG7 MYBs of angiosperms, such as At MYB12 . Mp MYB14 was induced by UVB, and it has previously been shown that Mp MYB14 overexpression activates the specific PAL and CHS genes induced by UVB ( Mapoly0014s0211 and Mapoly0021s0159 , respectively; Albert et al ., ). However, the UVB induction of flavone production was not altered in myb14 plants, and the changes that occurred in the transcript abundance of MYB14 in hy5 and rup1 plants did not suggest HY5 activation.…”

“…The marchantia genome contains at least some candidate downstream components of the angiosperm UVR8 signal transduction pathway such as COP1 and HY5 (Bowman et al ., ). Additionally, Mp MYB14 has been identified as an activator of flavonoid production in response to the abiotic stresses of increased white light exposure or nutrient deprivation (Albert et al ., ).…”

Untargeted liquid chromatography coupled with mass spectrometry reveals metabolic changes in nitrogen-deficient Isatis indigotica Fortune

“…Derived from the phenylpropanoid pathway, the flavonoid pathway is hypothesized to have evolved for protection against abiotic stresses by regulating the content of flavonoid (Albert et al, 2018). Flavonoids are also important bio-active compounds in medicinal plants, and they have variety of physiological effects, such as antioxidation, anti-cancer and anti-virus (Albert et al, 2018;Zhang et al, 2015).We found that the metabolic pathway of flavonoids was induced only in leaves by N-deficiency and low nitrogen. The accumulations of vitexin and xanthohumol were enhanced, by about 1.5 to 3-foldbetween low-N treatments and CK.…”