Abstract

MYB transcription factors have a wide range of functions in plant growth, hormone signaling, salt, and drought tolerances. In this study, two homologous transcription factors, PtrMYB55 and PtrMYB121, were isolated and their functions were elucidated. Tissue expression analysis revealed that PtrMYB55 and PtrMYB121 had a similar expression pattern, which had the highest expression in stems. Their expression continuously increased with the growth of poplar, and the expression of PtrMYB121 was significantly upregulated in the process. The full length of PtrMYB121 was 1395 bp, and encoded protein contained 464 amino acids including conserved R2 and R3 MYB domains. We overexpressed PtrMYB121 in Arabidopsis thaliana, and the transgenic lines had the wider xylem as compared with wild-type Arabidopsis. The contents of cellulose and lignin were obviously higher than those in wild-type materials, but there was no significant change in hemicellulose. Quantitative real-time PCR demonstrated that the key enzyme genes regulating the synthesis of lignin and cellulose were significantly upregulated in the transgenic lines. Furthermore, the effector-reporter experiment confirmed that PtrMYB121 bound directly to the promoters of genes relating to the synthesis of lignin and cellulose. These results suggest that PtrMYB121 may positively regulate the formation of secondary cell wall by promoting the synthesis of lignin and cellulose.

Highlights

  • The most abundant biological resource produced by woody plants is wood, which is widely used in traditional industries including lignum, papermaking, and pulping

  • The results indicate that PtrMYB121 can activate the expression of structural genes involved in the biosynthesis of lignin and cellulose and promote the accumulation of lignin and cellulose

  • We constructed a phylogenetic tree with PtrMYB55/121 and some MYB transcription factors (TFs) that have been reported to play key roles in secondary cell wall (SCW) biosynthesis from different species

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Summary

Introduction

The most abundant biological resource produced by woody plants is wood, which is widely used in traditional industries including lignum, papermaking, and pulping. Some NAC TFs have been found that function as master switches in various species of angiosperms, such as poplar, alfalfa, rice, eucalyptus, and birch, which suggests that these first-level master switch genes could conservatively regulate the SCW synthesis in vascular plants [15,16,17,18,19,20]. Another important gene family that regulates SCW biosynthesis is R2R3-MYB TFs, which belong to the second-level switch genes. The results indicate that PtrMYB121 can activate the expression of structural genes involved in the biosynthesis of lignin and cellulose and promote the accumulation of lignin and cellulose

Phylogenetic Analysis and Amino Acid Sequence Alignment of PtrMYB121
Tissue Expression Pattern Analysis of PtrMYB55 and PtrMYB121
Plant Materials
Phylogenetic Analysis
RNA Isolation and qRT-PCR Analysis
Arabidopsis Transformation
Phenotypic Observation of PtrMYB121-Overexpressing Lines in Arabidopsis
LUC Activity Assay
4.10. GenBank Accession Numbers of Genes Used in this Study
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