R2R3-MYB Transcription Factor Gene Research Articles

Silencing of SlMYB78-like Reduces the Tolerance to Drought and Salt Stress via the ABA Pathway in Tomato.

The MYB transcription factor family plays a crucial regulatory role in plant growth, development, biological progress, and stress responses. Here, we identified a R2R3-MYB transcription factor gene, SlMYB78-like, from tomato and characterized its function by gene silencing via RNA interference (RNAi). The results exhibited that the silencing of SlMYB78-like reduced the sensitivity of tomato seedlings to exogenous ABA. In addition, when exposed to drought and salt stresses, the RNAi lines grown in soil showed decreased tolerance, with lower ABA accumulation, relative water content, and chlorophyll content while displaying higher relative conductivity and malondialdehyde (MDA) content than the wild type. Moreover, the expression of genes related to chlorophyll biosynthesis, photosynthesis, and ABA biosynthesis/response were down-regulated in SlMYB78-like-silenced lines. Notably, the transcript level of SlCYP707-A2, which encodes a protein involved in ABA degradation, was up-regulated significantly after stresses. The transient expression assay Dual-luciferase (Dual-LUC) and a yeast one-hybrid (Y1H) assay demonstrated that SlMYB78-like bound to the promoter of SlCYP707-A2. Additionally, the physical interaction between SlMYB78-like and SlDREB3, which functioned in ABA signaling transduction, was identified through yeast two-hybrid (Y2H) and bimolecular fluorescence complementation (BiFC) assays. Collectively, our study illustrates that SlMYB78-like participates in the abiotic stress response via the ABA pathway.

Functional analysis of HpMYB72 showed its positive involvement in high-temperature resistance via repressing the expression of HpCYP73A

Global warming has led to occasional occurrence of extreme climates, especially summer high temperature, which constrains crops in growth and development. Pitaya (Hylocereus polyrhizus) characterizes in excellent tolerance to high temperature and drought stresses. Previously, a differentially expressed R2R3-MYB transcription factor gene, designated as HpMYB72, was identified in pitaya as exposure to high temperature. To elucidate the function of HpMYB72, currently, its spatiotemporal expression, as well as the roles involving in high-temperature response and regulating the downstream genes were conducted. The data from RT-qPCR and GUS reporter system showed that HpMYB72 was mainly expressed in rapidly developing tissues, particularly, in the flowers. It was activated by high temperature, and the coded proteins were accumulated in nucleus, indicating that HpMYB72 may act as a positive regulator involved in the high-temperature response of pitaya. Ectopic overexpression of HpMYB72 in Arabidopsis thaliana improved the growth performance and increased the germination rate as exposure to 42 °C; reduced the accumulation of reactive oxygen species under high-temperature stress thus alleviated the oxidative damage; increased the content of osmotic regulators, thereby relieved the water loss as exposure to high temperature. The available evidences comprehensively reflected that overexpression of HpMYB72 improved the tolerance of Arabidopsis against high temperature, supporting the hypothesis that HpMYB72 is a positive regulator of high-temperature response. The results of yeast one-hybrid assay and luciferase reporter system demonstrated that HpMYB72 bound directly to the promoter of pitaya cinnamate 4-hydroxylase gene HpCYP73A and inhibited its transcription. In this way, the NADPH which ought to be the substrate of cinnamate 4-hydroxylase was reassigned to ROS scavenging, and led the conversion of cinnamoyl-CoA to pinocembrin chalcone, which protects pitaya flowers from malformation under high temperature.

R2R3 MYB Transcription Factor GhMYB201 Promotes Cotton Fiber Elongation via Cell Wall Loosening and Very-Long-Chain Fatty Acid Synthesis.

Cotton fiber is the leading natural textile material, and fiber elongation plays an essential role in the formation of cotton yield and quality. Although a number of components in the molecular network controlling cotton fiber elongation have been reported, a lot of players still need to be functionally dissected to understand the regulatory mechanism of fiber elongation comprehensively. In the present study, an R2R3-MYB transcription factor gene, GhMYB201, was characterized and functionally verified via CRISPR/Cas9-mediated gene editing. GhMYB201 was homologous to Arabidopsis AtMYB60, and both coding genes (GhMYB201At and GhMYB201Dt) were preferentially expressed in elongating cotton fibers. Knocking-out of GhMYB201 significantly reduced the rate and duration of fiber elongation, resulting in shorter and coarser mature fibers. It was found that GhMYB201 could bind and activate the transcription of cell wall loosening genes (GhRDLs) and also β-ketoacyl-CoA synthase genes (GhKCSs) to enhance very-long-chain fatty acid (VLCFA) levels in elongating fibers. Taken together, our data demonstrated that the transcription factor GhMYB201s plays an essential role in promoting fiber elongation via activating genes related to cell wall loosening and VLCFA biosynthesis.

Identifying potential anthocyanin biosynthesis regulator in Chinese cherry by comprehensive genome-wide characterization of the R2R3-MYB transcription factor gene family

BackgroundChinese cherry [Cerasus pseudocerasus (Lindl.) G.Don] (syn. Prunus pseudocerasus Lindl.) is an economically important fruiting cherry species with a diverse range of attractive colors, spanning from the lightest yellow to the darkest black purple. However, the MYB transcription factors involved in anthocyanin biosynthesis underlying fruit color variation in Chinese cherry remain unknown.ResultsIn this study, we characterized the R2R3-MYB gene family of Chinese cherry by genome-wide identification and compared it with those of 10 Rosaceae relatives and Arabidopsis thaliana. A total of 1490 R2R3-MYBs were classified into 43 subfamilies, which included 29 subfamilies containing both Rosaceae MYBs and AtMYBs. One subfamily (S45) contained only Rosaceae MYBs, while three subfamilies (S12, S75, and S77) contained only AtMYBs. The variation in gene numbers within identical subfamilies among different species and the absence of certain subfamilies in some species indicated the species-specific expansion within MYB gene family in Chinese cherry and its relatives. Segmental and tandem duplication events primarily contributed to the expansion of Chinese cherry R2R3-CpMYBs. The duplicated gene pairs underwent purifying selection during evolution after duplication events. Phylogenetic relationships and transcript profiling revealed that CpMYB10 and CpMYB4 are involved in the regulation of anthocyanin biosynthesis in Chinese cherry fruits. Expression patterns, transient overexpression and VIGS results confirmed that CpMYB10 promotes anthocyanin accumulation in the fruit skin, while CpMYB4 acts as a repressor, inhibiting anthocyanin biosynthesis of Chinese cherry.ConclusionsThis study provides a comprehensive and systematic analysis of R2R3-MYB gene family in Chinese cherry and Rosaceae relatives, and identifies two regulators, CpMYB10 and CpMYB4, involved in anthocyanin biosynthesis in Chinese cherry. These results help to develop and utilize the potential functions of anthocyanins in Chinese cherry.

Transcription factor FveMYB117a inhibits axillary bud outgrowth by regulating cytokinin homeostasis in woodland strawberry.

Shoot branching affects plant architecture. In strawberry (Fragaria L.), short branches (crowns) develop from dormant axillary buds to form inflorescences and flowers. While this developmental transition contributes greatly to perenniality and yield in strawberry, its regulatory mechanism remains unclear and understudied. In the woodland strawberry (Fragaria vesca), we identified and characterized 2 independent mutants showing more crowns. Both mutant alleles reside in FveMYB117a, a R2R3-MYB transcription factor gene highly expressed in shoot apical meristems, axillary buds, and young leaves. Transcriptome analysis revealed that the expression of several cytokinin pathway genes was altered in the fvemyb117a mutant. Consistently, active cytokinins were significantly increased in the axillary buds of the fvemyb117a mutant. Exogenous application of cytokinin enhanced crown outgrowth in the wild type, whereas the cytokinin inhibitors suppressed crown outgrowth in the fvemyb117a mutant. FveMYB117a binds directly to the promoters of the cytokinin homeostasis genes FveIPT2 encoding an isopentenyltransferase and FveCKX1 encoding a cytokinin oxidase to regulate their expression. Conversely, the type-B Arabidopsis response regulators FveARR1 and FveARR2b can directly inhibit the expression of FveMYB117a, indicative of a negative feedback regulation. In conclusion, we identified FveMYB117a as a key repressor of crown outgrowth by inhibiting cytokinin accumulation and provide a mechanistic basis for bud fate transition in an herbaceous perennial plant.

OsMYB58 Negatively Regulates Plant Growth and Development by Regulating Phosphate Homeostasis.

Phosphate (Pi) starvation is a critical factor limiting crop growth, development, and productivity. Rice (Oryza sativa) R2R3-MYB transcription factors function in the transcriptional regulation of plant responses to various abiotic stresses and micronutrient deprivation, but little is known about their roles in Pi starvation signaling and Pi homeostasis. Here, we identified the R2R3-MYB transcription factor gene OsMYB58, which shares high sequence similarity with AtMYB58. OsMYB58 expression was induced more strongly by Pi starvation than by other micronutrient deficiencies. Overexpressing OsMYB58 in Arabidopsis thaliana and rice inhibited plant growth and development under Pi-deficient conditions. In addition, the overexpression of OsMYB58 in plants exposed to Pi deficiency strongly affected root development, including seminal root, lateral root, and root hair formation. Overexpressing OsMYB58 strongly decreased the expression of the rice microRNAs OsmiR399a and OsmiR399j. By contrast, overexpressing OsMYB58 strongly increased the expression of rice PHOSPHATE 2 (OsPHO2), whose expression is repressed by miR399 during Pi starvation signaling. OsMYB58 functions as a transcriptional repressor of the expression of its target genes, as determined by a transcriptional activity assay. These results demonstrate that OsMYB58 negatively regulates OsmiR399-dependent Pi starvation signaling by enhancing OsmiR399s expression.

Does an R2R3-MYB transcription factor affect anthurium spathe colour variation via regulation of vacuolar pH?

The anthurium is a popular cut flower worldwide having red, pink, coral, white, green, or brown spathes. There is a constant demand for new flower colours in the commercial market. Flower colour in plants is mainly determined by anthocyanins. Understanding anthocyanin variation and other factors affecting anthurium spathe colour is important for genetic engineering approaches. Therefore, our objectives were to assess the factors affecting colour variation of selected commercially available cut flower anthuriums and to determine the associated regulatory networks and transcription factors (TFs). Nineteen commercial cut flower anthurium cultivars were selected for this purpose. The colour of the spathe surface, anthocyanin location, anthocyanidin type and vacuolar pH were recorded. Anthocyanin associated Gene Network Model generation and analysis were carried out. The CIELAB colourimeter procedure indicated the colour variation among the selected 19 cultivars in terms of colour type, colour intensity, chroma, and hue angle. The location of anthocyanin was limited to mesophyll and epidermal cells. Cyanidin was detected in tested anthurium cultivars as the main anthocyanidin. The pH gradient in pigment extracts indicated a variation with a range of 4.6 to 4.94. The gene pathways of anthocyanin biosynthesis and transport were associated with that of the vacuolar pH/H+ pump according to Gene Network Model. Three pathways were regulated by an R2R3-MYB transcription factor. Although, cyanidin was the only pigment in all the tested cultivars, different pH levels by R2R3-MYB regulated V-H+ synthase was suggested to be the cause of the high colour variation in addition to the anthocyanidin type and location. Our results indicate the application of R2R3-MYB transcription factor genes for desirable vacuolar pH maintenance in genetic engineering of the blue anthurium in the future.

Simultaneous Promotion of Salt Tolerance and Phenolic Acid Biosynthesis in Salvia miltiorrhiza via Overexpression of Arabidopsis MYB12.

Transcription factors play crucial roles in regulating plant abiotic stress responses and physiological metabolic processes, which can be used for plant molecular breeding. In this study, an R2R3-MYB transcription factor gene, AtMYB12, was isolated from Arabidopsis thaliana and introduced into Salvia miltiorrhiza under the regulation of the CaMV35S promoter. The ectopic expression of AtMYB12 resulted in improved salt tolerance in S. miltiorrhiza; transgenic plants showed a more resistant phenotype under high-salinity conditions. Physiological experiments showed that transgenic plants exhibited higher chlorophyll contents, and decreased electrolyte leakage and O2- and H2O2 accumulation when subjected to salt stress. Moreover, the activity of reactive oxygen species (ROS)-scavenging enzymes was enhanced in S. miltiorrhiza via the overexpression of AtMYB12, and transgenic plants showed higher superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) activities compared with those of the wild type (WT) under salt stress, coupled with lower malondialdehyde (MDA) levels. In addition, the amount of salvianolic acid B was significantly elevated in all AtMYB12 transgenic hair roots and transgenic plants, and qRT-PCR analysis revealed that most genes in the phenolic acid biosynthetic pathway were up-regulated. In conclusion, these results demonstrated that AtMYB12 can significantly improve the resistance of plants to salt stress and promote the biosynthesis of phenolic acids by regulating genes involved in the biosynthetic pathway.

The R2R3-MYB transcription factor CsMYB42 regulates theanine biosynthesis in albino tea leaves

Theanine is a unique secondary metabolite in tea plants and contributes to the umami taste and health benefits of tea. However, theanine biosynthesis in tea plants is not fully understood, and its mechanism of transcriptional regulation remains poorly reported. Theanine content was significantly correlated with the expression of theanine biosynthesis-related gene CsGS1c and transcription factor CsMYB42 in different leaf positions and picking times, but there was no significant correlation in different tissues of albino tea plant ‘Anjibaicha’. This suggests that CsMYB42 may regulate CsGS1c to synthesize theanine in albino tea leaves, and the regulation is tissue specific. CsMYB42 is a nuclear-localized R2R3-MYB transcription factor gene with transcriptional activation activity. Yeast one-hybrid assay and electrophoretic mobility shift assay confirmed the direct binding of CsMYB42 to the promoter of CsGS1c. Luciferase assay showed that CsMYB42 activates the CsGS1c expression. Furthermore, the inhibition of CsMYB42 using an antisense oligonucleotide in tea leaves decreased CsGS1c expression and theanine content. These results indicate that CsMYB42 plays a crucial role in activating the expression of CsGS1c and may be involved in the biosynthesis of theanine in albino tea leaves. This study provides fresh insights into the tissue-specific regulation of theanine biosynthesis, which laid a foundation for breeding high-theanine tea plants.

Transcription factors MdMYC2 and MdMYB85 interact with ester aroma synthesis gene MdAAT1 in apple.

Volatile esters in apple (Malus domestica) fruit are the critical aroma components determining apple flavor quality. While the exact molecular regulatory mechanism remains unknown, jasmonic acid (JA) plays a crucial role in stimulating the synthesis of ester aromas in apples. In our study, we investigated the effects of methyl jasmonate (MeJA) on the production of ester aroma in apples. MeJA treatment significantly increased ester aroma synthesis, accompanied by the upregulation of several genes involved in the jasmonate pathway transduction. Specifically, expression of the gene MdMYC2, which encodes a transcription factor associated with the jasmonate pathway, and the R2R3-MYB transcription factor gene MdMYB85 increased upon MeJA treatment. Furthermore, the essential gene ALCOHOL ACYLTRANSFERASE 1 (MdAAT1), encoding an enzyme responsible for ester aroma synthesis, showed increased expression levels as well. Our investigation revealed that MdMYC2 and MdMYB85 directly interacted with the promoter region of MdAAT1, thereby enhancing its transcriptional activity. In addition, MdMYC2 and MdMYB85 directly bind their promoters and activate transcription. Notably, the interaction between MdMYC2 and MdMYB85 proteins further amplified the regulatory effect of MdMYB85 on MdMYC2 and MdAAT1, as well as that of MdMYC2 on MdMYB85 and MdAAT1. Collectively, our findings elucidate the role of the gene module consisting of MdMYC2, MdMYB85, and MdAAT1 in mediating the effects of JA and promoting ester aroma synthesis in apples.

Comparative transcriptome analysis reveals the involvement of an MYB transcriptional activator, SmMYB108, in anther dehiscence in eggplant.

Male sterility is a highly attractive agronomic trait as it effectively prevents self-fertilization and facilitates the production of high-quality hybrid seeds in plants. Timely release of mature pollen following anther dehiscence is essential for stamen development in flowering plants. Although several theories have been proposed regarding this, the specific mechanism of anther development in eggplant remains elusive. In this study, we selected an R2R3-MYB transcription factor gene, SmMYB108, that encodes a protein localized primarily in the nucleus by comparing the transcriptomics of different floral bud developmental stages of the eggplant fertile line, F142. Quantitative reverse transcription polymerase chain reaction revealed that SmMYB108 was preferentially expressed in flowers, and its expression increased significantly on the day of flowering. Overexpression of SmMYB108 in tobacco caused anther dehiscence. In addition, we found that SmMYB108 primarily functions as a transcriptional activator via C-terminal activation (amino acid 262-317). Yeast one-hybrid and dual-luciferase reporter assays revealed that genes (SmMYB21, SmARF6, and SmARF8) related to anther development targeted the SmMYB108 promoter. Overall, our results provide insights into the molecular mechanisms involved in the regulation of anther development by SmMYB108.

Balancing selection on an MYB transcription factor maintains the twig trichome color variation in Melastoma normale

BackgroundThe factors that maintain phenotypic and genetic variation within a population have received long-term attention in evolutionary biology. Here the genetic basis and evolution of the geographically widespread variation in twig trichome color (from red to white) in a shrub Melastoma normale was investigated using Pool-seq and evolutionary analyses.ResultsThe results show that the twig trichome coloration is under selection in different light environments and that a 6-kb region containing an R2R3 MYB transcription factor gene is the major region of divergence between the extreme red and white morphs. This gene has two highly divergent groups of alleles, one of which likely originated from introgression from another species in this genus and has risen to high frequency (> 0.6) within each of the three populations under investigation. In contrast, polymorphisms in other regions of the genome show no sign of differentiation between the two morphs, suggesting that genomic patterns of diversity have been shaped by homogenizing gene flow. Population genetics analysis reveals signals of balancing selection acting on this gene, and it is suggested that spatially varying selection is the most likely mechanism of balancing selection in this case.ConclusionsThis study demonstrate that polymorphisms on a single transcription factor gene largely confer the twig trichome color variation in M. normale, while also explaining how adaptive divergence can occur and be maintained in the face of gene flow.

Genome-wide analysis of the R2R3-MYB transcription factor gene family expressed in Juglans regia under abiotic and biotic stresses

MYB transcription factors are important in plant stress response. However, the MYB genes of walnut (Juglans regia), an important oil crop, have yet to be analyzed comprehensively. Using bioinformatics methods, 226 walnut R2R3-MYB genes were discovered at the genome level in this study. The genes were classified into 23 subgroups based on their evolutionary relationships and were unequally distributed across 16 walnut chromosomes. The genes of the same subgroup exhibit similar but not identical gene structure and conserved motifs. The promoter region carries several cis-acting elements connected with plant stress response. Tandem and segmental duplications primarily contributed to R2R3-MYB gene amplification in walnut. A total of 232, 54 and 14 walnut R2R3-MYB genes were homologous to Populus trichocarpa, Arabidopsis thaliana, and Zea mays genes, respectively. The results of publicly available transcriptome sequencing and real-time quantitative PCR analysis revealed that the Juglans R2R3-MYB genes were induced to express after Colletotrichum gloeosporioides infection and various abiotic stress treatments. Results of co-expression studies indicated that walnut R2R3-MYB genes may be involved in the regulation of the ICE1-CBF pathway in cold signal transduction. Our findings offer new insight into the potential role of R2R3-MYB transcription factors in biotic and abiotic stresses and provide a theoretical groundwork for the molecular mechanisms underlying walnut adaptation to such stress.

Genome-wide identification and expression pattern analysis of R2R3-MYB transcription factor gene family involved in puerarin biosynthesis and response to hormone in Pueraria lobata var. thomsonii

BackgroundR2R3-MYB transcription factors regulate secondary metabolism, stress responses and development in various plants. Puerarin is a bioactive ingredient and most abundant secondary metabolite isolated from Pueraria lobata. The biosynthesis of puerarin proceeds via the phenylpropanoid pathway and isoflavonoids pathway, in which 9 key enzymes are involved. The expression of these structural genes is under control of specific PtR2R3-MYB genes in different plant tissues. However, how PtR2R3-MYB genes regulates structural genes in puerarin biosynthesis remains elusive. This study mined the PtR2R3-MYB genes involved in puerarin biosynthesis and response to hormone in Pueraria lobata var. thomsonii.ResultsA total of 209 PtR2R3-MYB proteins were identified, in which classified into 34 subgroups based on the phylogenetic topology and the classification of the R2R3-MYB superfamily in Arabidopsis thaliana. Furtherly physical and chemical characteristics, gene structure, and conserved motif analysis were also used to further analyze PtR2R3-MYBs. Combining puerarin content and RNA-seq data, speculated on the regulated puerarin biosynthesis of PtR2R3-MYB genes and structural genes, thus 21 PtR2R3-MYB genes and 25 structural genes were selected for validation gene expression and further explore its response to MeJA and GSH treatment by using qRT-PCR analysis technique. Correlation analysis and cis-acting element analysis revealed that 6 PtR2R3-MYB genes (PtMYB039, PtMYB057, PtMYB080, PtMYB109, PtMYB115 and PtMYB138) and 7 structural genes (PtHID2, PtHID9, PtIFS3, PtUGT069, PtUGT188, PtUGT286 and PtUGT297) were directly or indirectly regulation of puerarin biosynthesis in ZG11. It is worth noting that after MeJA and GSH treatment for 12–24 h, the expression changes of most candidate genes were consistent with the correlation of puerarin biosynthesis, which also shows that MeJA and GSH have the potential to mediate puerarin biosynthesis by regulating gene expression in ZG11.ConclusionsOverall, this study provides a comprehensive understanding of the PtR2R3-MYB and will paves the way to reveal the transcriptional regulation of puerarin biosynthesis and response to phytohormone of PtR2R3-MYB genes in Pueraria lobata var. thomsonii.

A naturally-occurring phenomenon of flower color change during flower development in Xanthoceras sorbifolium.

Xanthoceras sorbifolium (yellowhorn) is originated in China and is a unique tree in northern China. Yellowhorn is very popular because of the gradual color change of its flower at different flower developmental stages. During flowering development, the color at the base of yellowhorn flower petals gradually changes from yellow to purple. The mechanism of this miraculous phenomenon is still unclear. Here we show that anthocyanin accumulation during flowering development is the main reason for this color change. RT-PCR results show that the expression level of a variety of anthocyanin biosynthesis genes changes in different flower developmental stages. Realtime results show that the expression changes of these anthocyanin biosynthesis genes are positively regulated by a cluster of R2R3-MYB transcription factor genes, XsMYB113s. Furthermore, the DNA methylation analysis showed that CHH methylation status on the transposon element near the XsMYB113-1 influence its transcript level during flowering development. Our results suggest that dynamic epigenetic regulation of the XsMYB113-1 leads to the accumulation of anthocyanins during yellowhorn flower color change. These findings reemphasize the role of epigenetic regulation in flower development and provide a foundation for further studies of epigenetic regulation in long-lived woody perennials.

Silencing of SlMYB50 affects tolerance to drought and salt stress in tomato

High salinity and drought stresses often cause plants to produce ROS, including hydrogen peroxide (H2O2) and superoxide (O2−), which interfere with plant growth and affect crop yield. The transcription factors of the MYB family are involved in responses to biotic and abiotic stresses. Here, we isolated the R2R3-MYB transcription factor gene SlMYB50 and found that silencing of SlMYB50 increased resistance to PEG 6000, mannitol and salt. In addition, the resistance of transgenic tomatoes increased under high salt and drought stress. After stress treatment, the relative water content, chlorophyll content (critical for carbon fixation) and root vitality of the SlMYB50-RNAi lines were higher than those of the wild-type (WT). The opposite was true the water loss rate, relative conductivity, and MDA (as a sign of cell wall disruption). Under drought stress conditions, SlMYB50-silenced lines exhibited less H2O2 and less O2− accumulation, as well as higher CAT enzyme activity, than were exhibited by the WT. Notably, after stress treatment, the expression levels of chlorophyll-synthesis-related, flavonoid-synthesis-related, carotenoid-related, antioxidant-enzyme-related and ABA-biosynthesis-related genes were all upregulated in SlMYB50-silenced lines compared to those of WT. A dual-luciferase reporter system was used to verify that SlMYB50 could bind to the CHS1 promoter. In summary, this study identified essential roles for SlMYB50 in regulating drought and salt tolerance.

Tropaeolum majus R2R3 MYB Transcription Factor TmPAP2 Functions as a Positive Regulator of Anthocyanin Biosynthesis.

Anthocyanins are an important group of water-soluble and non-toxic natural pigments with antioxidant and anti-inflammatory properties that can be found in flowers, vegetables, and fruits. Anthocyanin biosynthesis is regulated by several different types of transcription factors, including the WD40-repeat protein Transparent Testa Glabra 1 (TTG1), the bHLH transcription factor Transparent Testa 8 (TT8), Glabra3 (GL3), Enhancer of GL3 (EGL3), and the R2R3 MYB transcription factor Production of Anthocyanin Pigment 1 (PAP1), PAP2, MYB113, and MYB114, which are able to form MYB-bHLH-WD40 (MBW) complexes to regulate the expression of late biosynthesis genes (LBGs) in the anthocyanin biosynthesis pathway. Nasturtium (Tropaeolum majus) is an edible flower plant that offers many health benefits, as it contains numerous medicinally important ingredients, including anthocyanins. By a comparative examination of the possible anthocyanin biosynthesis regulator genes in nasturtium varieties with different anthocyanin contents, we found that TmPAP2, an R2R3 MYB transcription factor gene, is highly expressed in “Empress of India”, a nasturtium variety with high anthocyanin content, while the expression of TmPAP2 in Arabidopsis led to the overproduction of anthocyanins. Protoplast transfection shows that TmPAP2 functions as a transcription activator; consistent with this finding, some of the biosynthesis genes in the general phenylpropanoid pathway and anthocyanin biosynthesis pathway were highly expressed in “Empress of India” and the 35S:TmPAP2 transgenic Arabidopsis plants. However, protoplast transfection indicates that TmPAP2 may not be able to form an MBW complex with TmGL3 and TmTTG1. These results suggest that TmPAP2 may function alone as a key regulator of anthocyanin biosynthesis in nasturtiums.

SmMYB4 Is a R2R3-MYB Transcriptional Repressor Regulating the Biosynthesis of Phenolic Acids and Tanshinones in Salvia miltiorrhiza.

Salvia miltiorrhiza Bunge is one of the most famous traditional Chinese medicinal plants. The two most important classes of pharmaceutically relevant compounds in S. miltiorrhiza are phenolic acids and tanshinones. The MYB family of transcription factors may efficiently regulate the secondary metabolism in plants. In this study, a subgroup 4 R2R3MYB transcription factor gene, SmMYB4, was isolated from S. miltiorrhiza and functionally characterized using overexpression and a RNAi-mediated silencing. We achieved a total of six overexpressions and eight RNAi transgenic lines from the Agrobacterium leaf disc method. The content of the total phenolics, rosmarinic acid, and salvianolic acid B markedly decreased in the SmMYB4-overexpressing lines but increased in the SmMYB4-RNAi lines. The content of the total tanshinones, cryptotanshinone, and tanshinone IIA decreased in the SmMYB4-overexpressing transgenic lines but increased in the SmMYB4-RNAi lines. A gene expression analysis demonstrated that SmMYB4 negatively regulated the transcription of the critical enzyme genes involved in the phenolic acid and tanshinone biosynthesis. The genetic control of this transcriptional repressor may be used to improve the content of these bioactive compounds in the cultivated S. miltiorrhiza.

MsMYB741 is involved in alfalfa resistance to aluminum stress by regulating flavonoid biosynthesis.

Aluminum (Al) toxicity severely restricts plant growth in acidic soils (pH < 5.0). In this study, an R2R3-MYB transcription factor (TF) gene, MsMYB741, was cloned from alfalfa. Its function and gene regulatory pathways were studied via overexpression and RNA interference of MsMYB741 in alfalfa seedlings. Results showed that root elongation increased as a result of MsMYB741 overexpression (MsMYB741-OE) and decreased with MsMYB741 RNA interference (MsMYB741-RNAi) in alfalfa seedlings compared with the wild-type under Al stress. These were attributed to the reduced Al content in MsMYB741-OE lines, and increased Al content in MsMYB741-RNAi lines. MsMYB741 positively activated the expression of phenylalanine ammonia-lyase 1 (MsPAL1) and chalcone isomerase (MsCHI) by binding to MYB and ABRE elements in their promoters, respectively, which directly affected flavonoid accumulation in roots and secretion from root tips in plants under Al stress, eventually affecting Al accumulation in alfalfa. Additionally, MsABF2 TF directly activated the expression of MsMYB741 by binding to the ABRE element in its promoter. Taken together, our results indicate that MsMYB741 transcriptionally activates MsPAL1 and MsCHI expression to increase flavonoid accumulation in roots and secretion from root tips, leading to increased resistance of alfalfa to Al stress.

The Indole-3-Acetamide-Induced Arabidopsis Transcription Factor MYB74 Decreases Plant Growth and Contributes to the Control of Osmotic Stress Responses.

The accumulation of the auxin precursor indole-3-acetamide (IAM) in the ami1 mutant has recently been reported to reduce plant growth and to trigger abiotic stress responses in Arabidopsis thaliana. The observed response includes the induction of abscisic acid (ABA) biosynthesis through the promotion of NCED3 expression. The mechanism by which plant growth is limited, however, remained largely unclear. Here, we investigated the transcriptional responses evoked by the exogenous application of IAM using comprehensive RNA-sequencing (RNA-seq) and reverse genetics approaches. The RNA-seq results highlighted the induction of a small number of genes, including the R2R3 MYB transcription factor genes MYB74 and MYB102. The two MYB factors are known to respond to various stress cues and to ABA. Consistent with a role as negative plant growth regulator, conditional MYB74 overexpressor lines showed a considerable growth reduction. RNA-seq analysis of MYB74 mutants indicated an association of MYB74 with responses to osmotic stress, water deprivation, and seed development, which further linked MYB74 with the observed ami1 osmotic stress and seed phenotype. Collectively, our findings point toward a role for MYB74 in plant growth control and in responses to abiotic stress stimuli.