Nitrogen deficiency enhances expression of specific MYB and bHLH transcription factors and accumulation of end products in the flavonoid pathway

Abstract

Expression of regulators of the flavonoid pathway was examined in Arabidopsis thaliana wild type and pap1D plants, the latter being a T-DNA activation-tagged line over-expressing the PAP1/MYB75 gene which is a positive regulator of the pathway. Anthocyanin accumulation was induced in plants grown in soil, on agar plates, and hydroponics by withdrawing nitrogen from the growth medium. The agar-grown seedlings and rosette stage plants in hydroponics were further explored, and showed that nitrogen deficiency resulted in the accumulation of not only anthocyanins, but also flavonols. The examination of transcript levels showed that the general flavonoid pathway regulators PAP1 and PAP2 were up-regulated in response to nitrogen deficiency in wild type as well as pap1D plants. Interestingly, PAP2 responded much stronger to nitrogen deficiency than PAP1, 200- and 6-fold increase in transcript levels, respectively, for wild-type seedlings. In rosette leaves the increase was 900-fold for PAP2 and 6-fold for PAP1. At least three different bHLH domain transcription factors promote anthocyanin synthesis, and transcripts for one of these, i.e. GL3 were found to be sixfold enhanced by nitrogen deficiency in rosette leaves. The MYB12 transcription factor, known to regulate flavonol synthesis, was slightly induced by nitrogen deficiency in seedlings. In conclusion, four out of eight regulators involved in the flavonoid pathway showed an enhanced expression from 2 to 1,000 times in response to nitrogen deficiency. Together with MYB factors, especially PAP2, GL3 appears to be the BHLH partner for anthocyanin accumulation in response to nitrogen deficiency.

The Arabidopsis transcription factor MYB112 promotes anthocyanin formation during salinity and under high light stress

“…Our result is in agreement with previously published global transcriptome data on Suc-responsive genes (Solfanelli et al, 2006;Osuna et al, 2007). Nitrogen deficiency also enhances expression of specific MYB and bHLH TFs and accumulation of end products of the flavonoid pathway (Lea et al, 2007;Rubin et al, 2009). However, MYB112 transcript abundance in plants grown for 6 d on medium with no nitrogen source was comparable with the transcript level in control plants grown on full (nitrogen-sufficient) medium, whereas in the same experiment, as anticipated, PAP1 expression increased approximately 8-fold (Fig.…”

“…However, although salinity stress is well known to lead to an accumulation of anthocyanin in a number of species, including crops and vegetables, such as tomato, maize, sugarcane, and many others (Kaliamoorthy and Rao, 1994;Piao et al, 2001;Wahid and Ghazanfar, 2006;Keutgen and Pawelzik, 2007;Roychoudhury et al, 2008;Matus et al, 2010), the regulatory mechanisms underlying this phenomena have not been studied intensively to date. Herein, we show that MYB112 expression is induced by salinity stress, whereas its expression is largely unaffected by nitrogen limitation, and sugar levels in contrast to many of the known transcriptional regulators of flavonoid/anthocyanin biosynthesis (Scheible et al, 2004;Misson et al, 2005;Lea et al, 2007;Morcuende et al, 2007;Lillo et al, 2008). We further illustrate that salinity-induced accumulation of anthocyanin is impaired in myb112 mutants but stimulated in 35S: MYB112 overexpressors, indicating that MYB112 plays a critical role during salt-induced anthocyanin accumulation.…”

“…Accumulation of anthocyanins has been reported to occur under a number of stresses, and the effects of nutrient (nitrogen or phosphorous) deprivation and light quality and quantity have been subject to the most attention in the past; several TFs have been shown to be involved in this response, including members of the MYB and bHLH families (Lea et al, 2007;Lillo et al, 2008;Stracke et al, 2010). However, although salinity stress is well known to lead to an accumulation of anthocyanin in a number of species, including crops and vegetables, such as tomato, maize, sugarcane, and many others (Kaliamoorthy and Rao, 1994;Piao et al, 2001;Wahid and Ghazanfar, 2006;Keutgen and Pawelzik, 2007;Roychoudhury et al, 2008;Matus et al, 2010), the regulatory mechanisms underlying this phenomena have not been studied intensively to date.…”

Members of theLBDFamily of Transcription Factors Repress Anthocyanin Synthesis and Affect Additional Nitrogen Responses inArabidopsis

“…can antagonize the LBD-mediated N/NO 3 2 repression of PAP1 but not the repression of PAP2 (Figure 10). Consistent with this, PAP1 was proposed to have a key role in light and sucrose induction of anthocyanin biosynthesis in Arabidopsis (Teng et al, 2005;Solfanelli et al, 2006;Cominelli et al, 2008), whereas PAP2 appears to be more important in the N/NO 3 2 regulation of anthocyanin biosynthesis (Lea et al, 2007). The fact that PAP1 expression in sugar-or P-stressed LBD37 OX seedlings is still ;10-fold lower than in PAP1-overexpressing pap1-D lines (see Supplemental Figure 12 online) might explain their inability to produce high levels of anthocyanin.…”

Cloning and characterization of ChiMYB in Chrysanthemum indicum with an emphasis on salinity stress tolerance

“…MYB proteins are one of the largest families of plant transcription factors (Tang and Chen, 2014). Moreover, most MYB members belong to the R2R3-MYB type (Shu et al, 2012b), and they are involved in the regulation of plant secondary metabolism and responses to different stresses (Uimari and Strommer, 1997;Hoeren et al, 1998;Lea et al, 2007;. Different members of the MYB family may have varying tempo-spatial expression patterns, and they may function differently in plants (reference needed).…”