Abstract
The MYB (v-myb avian myeloblastosis viral oncogene homolog) family is one of the largest transcription factor families in plants, and is widely involved in the regulation of plant metabolism. In this study, we show that a MYB4 transcription factor, BpMYB4, identified from birch (Betula platyphylla Suk.) and homologous to EgMYB1 from Eucalyptus robusta Smith and ZmMYB31 from Zea mays L. is involved in secondary cell wall synthesis. The expression level of BpMYB4 was higher in flowers relative to other tissues, and was induced by artificial bending and gravitational stimuli in developing xylem tissues. The expression of this gene was not enriched in the developing xylem during the active season, and showed higher transcript levels in xylem tissues around sprouting and near the dormant period. BpMYB4 also was induced express by abiotic stress. Functional analysis indicated that expression of BpMYB4 in transgenic Arabidopsis (Arabidopsis thaliana) plants could promote the growth of stems, and result in increased number of inflorescence stems and shoots. Anatomical observation of stem sections showed lower lignin deposition, and a chemical contents test also demonstrated increased cellulose and decreased lignin content in the transgenic plants. In addition, treatment with 100 mM NaCl and 200 mM mannitol resulted in the germination rate of the over-expressed lines being higher than that of the wild-type seeds. The proline content in transgenic plants was higher than that in WT, but MDA content was lower than that in WT. Further investigation in birch using transient transformation techniques indicated that overexpression of BpMYB4 could scavenge hydrogen peroxide and O2.– and reduce cell damage, compared with the wild-type plants. Therefore, we believe that BpMYB4 promotes stem development and cellulose biosynthesis as an inhibitor of lignin biosynthesis, and has a function in abiotic stress resistance.
Highlights
As a ubiquitous transcription factor in plants and animals, MYB proteins are widely involved in the regulation of developmental and metabolic changes in plants
The results can help further understand the molecular mechanism of secondary growth processes and abiotic stress responses regulated by MYB transcription factors in woody plants
A phylogenetic tree (Figure 1B) analysis showed that BpMYB4 was more similar to EgMYB1, which is a inhibitory of lignin biosynthesis, compared with Antirrhinum AmMYB308 and maize ZmMYB31 and ZmMYB42
Summary
As a ubiquitous transcription factor in plants and animals, MYB proteins are widely involved in the regulation of developmental and metabolic changes in plants. NAC-MYB-based transcriptional regulation of secondary cell wall biosynthesis in land plants is widely known. AtMYB26 regulates the synthesis of secondary cell walls through NST1 (NAC SECONDARY WALL THICKENING PROMOTING FACTOR 1) and NST2, and its overexpression can lead to ectopic deposition of secondary cell walls (Mitsuda et al, 2005; Yang et al, 2007). Overexpression of PtMYB4 in tobacco (Nicotiana tabacum L.) plants can induce the expression of some lignin biosynthesis genes and cause abnormal deposition of lignin and secondary wall thickening (Patzlaff et al, 2003a). PtrMYB003 and PtrMYB020 in Populus are homologous with Arabidopsis AtMYB46 and are expressed in secondary xylem; when overexpressed in Arabidopsis they activate the biosynthesis of cellulose, hemicellulose, and lignin (Mccarthy et al, 2010). AtMYB75 mainly regulates the biosynthesis of anthocyanins, but overexpression of this protein leads to a slight increase in lignin accumulation, indicating that the protein is involved in the regulation of lignin biosynthesis (Borevitz et al, 2000)
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