Xiaofen Liu

The MrWD40-1 Gene of Chinese Bayberry ( Myrica rubra ) Interacts with MYB and bHLH to Enhance Anthocyanin Accumulation

Anthocyanins are important for fruits as they contribute not only to fruit color but also to human health. Anthocyanin biosynthesis is transcriptionally regulated by the MYB–bHLH–WD40 transcription complex. For Chinese bayberry (Myrica rubra), the MYB and bHLH regulating anthocyanin accumulation, named as MrMYB1 and MrbHLH1, respectively, have been isolated previously. In this study, by searching and assembling the sequences available in the RNA-Seq database of Chinese bayberry, 60 WD40 members were obtained. Through phylogenetic analysis of these members with those related to anthocyanin biosynthesis regulation in other plants, unigenes 803 and 11128, designated as MrWD40-1 and MrWD40-2, respectively, have been isolated as the putative WD40 members regulating anthocyanin biosynthesis. However, positive correlation was observed between the anthocyanin accumulation and the expression patterns of MrWD40-1 but not MrWD40-2, both during fruit development, and in different tissues or cultivars of Chinese bayberry. Tobacco transient assays indicated that the ternary expression of MrMYB1–MrbHLH1–MrWD40-1 induced anthocyanin accumulation earlier and stronger than with binary expression of MrMYB1–MrbHLH1 in the absence of MrWD40-1. Compared with the enhancement effect on anthocyanin biosynthesis of MrWD40-1, MrWD40-2 could not improve the anthocyanin accumulation even with MrMYB1 and MrbHLH1, although the highly conserved four WD repeat motifs were also present in MrWD40-2. Moreover, it was observed that MrWD40-1 physically interacted with both MrMYB1 and MrbHLH1 according to yeast two-hybrid analysis. These results indicated that MrWD40-1, but not MrWD40-2, is the member regulating anthocyanin biosynthesis in Chinese bayberry through the formation of a ternary complex with MrMYB1 and MrbHLH1.

The role of MrbHLH1 and MrMYB1 in regulating anthocyanin biosynthetic genes in tobacco and Chinese bayberry (Myrica rubra) during anthocyanin biosynthesis

Anthocyanins, being important for both plant functions and human health, were transcriptionally regulated by the MYB–bHLH–WD40 transcription complex. The key MYB regulator for Chinese bayberry (Myrica rubra), MrMYB1, has been characterized in previous studies, while the specific bHLH partner(s) are unknown. In this study, MrbHLH1 and MrbHLH2 were isolated based on their homology to known plant bHLHs involved in anthocyanin biosynthesis regulation. Coordinate expression of MrbHLH1 with MrMYB1 and the anthocyanin biosynthetic genes was observed during fruit development, while MrbHLH2 showed a weaker correlation. Further transient assays in tobacco leaves suggested that MrbHLH1, but not MrbHLH2, was associated with MrMYB1 and triggered significant anthocyanin production. The lack of function of the MrbHLH2 in anthocyanin biosynthesis regulation suggested that different MrbHLH genes within the same phylogenic subfamily have different functions. Overexpression of MrMYB1 and MrbHLH1 in tobacco confirmed the crucial role of MrMYB1–MrbHLH1 in anthocyanin biosynthesis and all of the structural genes from NtCHS were up-regulated by the complex. Dual luciferase assays, however, indicated that MrMYB1 and MrbHLH1 selectively activated five of the eight promoters of biosynthetic genes from bayberry (MrCHI, MrF3′H, MrDFR1, MrANS, MrUFGT), although expression levels of all eight biosynthetic genes including MrCHS and downstream genes were coordinately increased during fruit ripening. Moreover, the interaction between MrbHLH1 and MrMYB1 was confirmed by yeast two-hybrid assay. In conclusion, MrbHLH1, but not MrbHLH2, was the essential partner of MrMYB1 during anthocyanin biosynthesis regulation in tobacco and bayberry, however, the biosynthetic genes in these two species responded differently to the MrMYB1–MrbHLH1 complex.

Differential activation of anthocyanin biosynthesis in Arabidopsis and tobacco over-expressing an R2R3 MYB from Chinese bayberry

MrMYB1, an R2R3 MYB transcription factor (TF) gene associated with anthocyanin biosynthesis in Chinese bayberry (Myrica rubra Sieb. and Zucc.), was introduced into Arabidopsis and tobacco (Nicotiana tabacum) under the control of the CaMV 35S promoter. Overexpression of MrMYB1 induced anthocyanin accumulation in all tissues of Arabidopsis as well as in petals, ovaries and young seeds of tobacco, but not in tobacco leaves. The anthocyanin biosynthetic pathway, including chalcone synthase (CHS), dihydroflavonol 4-reductase (DFR) and anthocyanidin synthase (ANS), and the basic helix-loop-helix (bHLH) transcriptional partner TRANSPARENT TESTA8 (TT8), were up-regulated significantly in MrMYB1-overexpressing Arabidopsis. In MrMYB1-overexpressing tobacco petals, ovaries and young seeds, anthocyanin biosynthetic genes and bHLH partners NtAn1a and NtAn1b, were up-regulated. In contrast, high expression of MrMYB1 in transgenic tobacco leaves did not induce the expression of anthocyanin biosynthesis. Unlike in petals and ovaries, the foliar transcript level of NtAn1a and NtAn1b was extremely low and not stimulated by MrMYB1 transformation. These results show that higher expression of an endogenous bHLH partner, either intrinsically or stimulated by exogenous gene transformation, is required for anthocyanin production in plant tissues, and the different abundance in endogenous bHLH transcript accounts for differential accumulation of anthocyanin in Arabidopsis and tobacco leaves. These findings demonstrate that higher levels of expression of an endogenous bHLH partner, either intrinsically or following genetic transformation, are required for anthocyanin production in plant tissues. Moreover, differences in levels of endogenous bHLH transcripts account for observed differential accumulation of anthocyanin in leaves of Arabidopsis and tobacco.

A Novel bHLH Transcription Factor Involved in Regulating Anthocyanin Biosynthesis in Chrysanthemums (Chrysanthemum morifolium Ramat.)

Chrysanthemums (Chrysanthemum morifolium Ramat.) exhibit a variety of flower colors due to their differing abilities to accumulate anthocyanins. One MYB member, CmMYB6, has been verified as a transcription regulator of chrysanthemum genes involved in anthocyanin biosynthesis; however, the co-regulators for CmMYB6 remain unclear in chrysanthemum. Here, the expression pattern of CmbHLH2, which is clustered in the IIIf bHLH subgroup, was shown to be positively correlated with the anthocyanin content of cultivars with red, pink and yellow flower colors, respectively. CmbHLH2 significantly upregulated the CmDFR promoter and triggered anthocyanin accumulation when co-expressed with CmMYB6. Yeast one-hybrid analyses indicated that CmbHLH2 was able to bind directly to the CmDFR promoter. Moreover, yeast two-hybrid assays indicated protein-protein interaction between CmbHLH2 and CmMYB6. These results suggest that CmbHLH2 is the essential partner for CmMYB6 in regulating anthocyanin biosynthesis in chrysanthemum.

Isolation and Expression of NAC Genes during Persimmon Fruit Postharvest Astringency Removal

NAC genes have been characterized in numerous plants, where they are involved in responses to biotic and abiotic stress, including low oxygen stress. High concentration of CO2 is one of the most effective treatments to remove astringency of persimmon fruit owing to the action of the accumulated anoxia metabolite acetaldehyde. In model plants, NAC genes have been identified as being responsive to low oxygen. However, the possible relationship between NAC transcription factors and persimmon astringency removal remains unexplored. In the present research, treatment with a high concentration of CO2 (95%) effectively removed astringency of “Mopan” persimmon fruit by causing decreases in soluble tannin. Acetaldehyde content increased in response to CO2 treatment concomitantly with astringency removal. Using RNA-seq and Rapid amplification of cDNA ends (RACE), six DkNAC genes were isolated and studied. Transcriptional analysis indicated DkNAC genes responded differentially to CO2 treatment; DkNAC1, DkNAC3, DkNAC5 and DkNAC6 were transiently up-regulated, DkNAC2 was abundantly expressed 3 days after treatment, while the DkNAC4 was suppressed during astringency removal. It is proposed that DkNAC1/3/5/6 could be important candidates as regulators of persimmon astringency removal and the roles of other member are also discussed.

Citrus CitNAC62 cooperates with CitWRKY1 to participate in citric acid degradation via up-regulation of CitAco3

Two novel transcription factors, CitNAC62 and CitWRKY1, were involved in citric acid degradation in citrus fruit, potentially via enhanced expression of CitAco3.

Techniques for rapid preparation of tomato leaf DNA and its application in real-time quantitative PCR-based transgene detection

Using tomato (Solanum lycopersicum L. cv. Micro-Tom) leaf as material, a simple and rapid DNA preparation protocol was established. This method required only 2-20 mm2 leaf with only one extraction solution and involved one pipetation and one centrifugation each. No precipitation was required. The suitable volume of prepared DNA solution, as PCR template, for real-time quantitative PCR was determined to be 0.10.2 μL in 12.5 μL final reaction volume. The excessive template DNA solution was confirmed to reduce PCR efficiency and even can result in PCR failure. This technique for rapid preparation of DNA and a compatible real-time quantitative PCR were successfully applied in transgene detection of tomato plants.

SIMYB1 and SIMYB2, two new MYB genes from tomato, transcriptionally regulate cellulose biosynthesis in tobacco

Abstract Cellulose, a major constituent of plant biomass, is synthesized by a cellulose synthase complex. It has been demonstrated that MYB genes transcriptionally regulate cellulose synthase in Arabidopsis. However, little is known about this process in tomato. Here, two MYB (SIMYB1/2) and three cellulose synthase (CESA) (SICESA4/5/6) genes were isolated. SIMYB1/2 and SICESA4/5/6 accumulation was found to correspond to cellulose accumulation in different tissues of tomato. Dual luciferase assays indicated that these two MYBs were transcriptional activators that interact with promoters of SICESA4/5/6. Moreover, SIMYB2 could also activate promoters of SIMYB1/2, suggesting the possible underlying auto-activation mechanisms for MYB transcription factors. Transient over-expression of SIMYB1/2 in Nicotiana tabacum up-regulated tobacco endogenous NtCESA genes and increased cellulose accumulation. The function of SIMYB1/2 was further investigated using stable transformation and the results indicated that N. tabacum lines heterologous expressing SIMYB1/2 displayed a pleiotropic phenotype, long and narrow leaves, with NtCESA induced and significant increase of cellulose. In conclusion, our data suggest that tomato SIMYB1/2 have transcriptional regulatory roles in cellulose biosynthesis and SIMYB2 was more effective than SIMYB1, which may due to the transcriptional activation by SIMYB2 on SIMYB1 and itself.

An ETHYLENE RESPONSE FACTOR-MYB Transcription Complex Regulates Furaneol Biosynthesis by Activating QUINONE OXIDOREDUCTASE Expression in Strawberry

Fragaria × ananassa quinone oxidoreductase, which catalyzes the final step in furaneol biosynthesis in strawberry, is transcriptionally up-regulated by a complex consisting of an ethylene response factor and MYB during ripening. 4-Hydroxy-2,5-dimethyl-3(2H)-furanone is a major contributor to the aroma of strawberry (Fragaria × ananassa) fruit, and the last step in its biosynthesis is catalyzed by strawberry quinone oxidoreductase (FaQR). Here, an ethylene response factor (FaERF#9) was characterized as a positive regulator of the FaQR promoter. Linear regression analysis indicated that FaERF#9 transcript levels were correlated significantly with both FaQR transcripts and furanone content in different strawberry cultivars. Transient overexpression of FaERF#9 in strawberry fruit significantly increased FaQR expression and furaneol production. Yeast one-hybrid assays, however, indicated that FaERF#9 by itself did not bind to the FaQR promoter. An MYB transcription factor (FaMYB98) identified in yeast one-hybrid screening of the strawberry cDNA library was capable of both binding to the promoter and activating the transcription of FaQR by ∼5.6-fold. Yeast two-hybrid assay and bimolecular fluorescence complementation confirmed a direct protein-protein interaction between FaERF#9 and FaMYB98, and in combination, they activated the FaQR promoter 14-fold in transactivation assays. These results indicate that an ERF-MYB complex containing FaERF#9 and FaMYB98 activates the FaQR promoter and up-regulates 4-hydroxy-2,5-dimethyl-3(2H)-furanone biosynthesis in strawberry.