EuMYB308 regulates lignin accumulation by targeting EuLAC17 in Eucalyptus urophylla

Abstract

It is known that laccase genes are involved in lignin synthesis. Eucalyptus is an important timber species; functional studies of specific laccase members and their upstream regulatory factors in Eucalyptus are incomplete, and the mechanism of lignin content variation in polyploid plants remains unclear. Therefore, in this study, we investigated the function of EuLAC17 by overexpressing it in tobaccos and the result showed the lignin content in transgenic tobacco increased significantly. Further, yeast one hybrid sequencing was used to identify a series of potential regulatory factors of EuLAC17, among which EuMYB308 showed the most significant correlation with EuLAC17. Yeast one hybrid, dual-luciferase reporter gene assay and electrophoretic mobility shift assay jointly verified that EuMYB308 could directly target the EuLAC17 promoter and repress its expression. In addition, overexpression of EuMYB308 resulted in significant reductions in plant growth, xylem cell lumen area, cell wall thickness and lignin content. Transcriptome sequencing showed that lignin biosynthesis genes including laccase genes were significantly differential expression in transgenic plants compared with wild-type plants. In triploid Eucalyptus urophylla, the expression of EuMYB308 was significantly upregulated, which may enhance the inhibition of EuLAC17 and thus reduce its expression level in triploid, which is one possible reason for the reduced lignin content in triploid E. urophylla. This study provides important insights into transcriptional regulation of lignin biosynthesis in Eucalyptus, and also contributes to revealing the genetic mechanism of lignin content variation in polyploid plants, which are of great significance for promoting the improvement of wood quality in forest trees and polyploid breeding.