Wood Transcriptome Profiling Identifies Critical Pathway Genes of Secondary Wall Biosynthesis and Novel Regulators for Vascular Cambium Development in Populus

Abstract

Wood, the most abundant biomass on Earth, is composed of secondary xylem differentiated from vascular cambium. However, the underlying molecular mechanisms of wood formation remain largely unclear. To gain insight into wood formation, we performed a series of wood-forming tissue-specific transcriptome analyses from a hybrid poplar (Populus alba × P. glandulosa, clone BH) using RNA-seq. Together with shoot apex and leaf tissue, cambium and xylem tissues were isolated from vertical stem segments representing a gradient of secondary growth developmental stages (i.e., immature, intermediate, and mature stem). In a comparative transcriptome analysis of the ‘developing xylem’ and ‘leaf’ tissue, we could identify critical players catalyzing each biosynthetic step of secondary wall components (e.g., cellulose, xylan, and lignin). Several candidate genes involved in the initiation of vascular cambium formation were found via a co-expression network analysis using abundantly expressed genes in the ‘intermediate stem-derived cambium’ tissue. We found that transgenic Arabidopsis plants overexpressing the PtrHAM4-1, a GRAS family transcription factor, resulted in a significant increase of vascular cambium development. This phenotype was successfully reproduced in the transgenic poplars overexpressing the PtrHAM4-1. Taken together, our results may serve as a springboard for further research to unravel the molecular mechanism of wood formation, one of the most important biological processes on this planet.

Quantitative profiling of N6-methyladenosine at single-base resolution in stem-differentiating xylem of Populus trichocarpa using Nanopore direct RNA sequencing

“…6 c). For example, PARVUS-L-2 is galacturonosyltransferase-like 1, which shows tissue-specific expression in stem-derived developing xylem [ 25 ]. Our DRS data showed that this secondary wall biosynthetic gene included two polyadenylation sites with different poly(A) length (Fig.…”

MYB Transcription Factors and Its Regulation in Secondary Cell Wall Formation and Lignin Biosynthesis during Xylem Development

“…Most of our understanding of secondary growth comes from the study of Arabidopsis [ 129 ]. However, secondary growth in woody perennials is different from that in Arabidopsis roots or hypocotyls [ 130 ].…”

Transcriptional and Post-transcriptional Regulation of Lignin Biosynthesis Pathway Genes in Populus

“…Broad expression evidence from key enzymes in the lignin biosynthetic pathway provides a hypothetical foundation for their functions in various tissues. For example, Kim et al (2019) performed a series of wood-forming tissue-specific transcriptome analyses from a hybrid poplar and identified critical pathway genes for secondary wall biosynthesis in mature developing xylem. Wood formation is a process of plant secondary growth, which originates from the cambium meristem cells, eventually forming a tree's main stem or truck.…”