Xylem Cell Wall Formation in Pioneer Roots and Stems of Populus trichocarpa (Torr. & Gray)

Abstract

Regulation of gene expression, as determined by the genetics of the tree species, is a major factor in determining wood quality. Therefore, the identification of genes that play a role in xylogenesis is extremely important for understanding the mechanisms shaping the plant phenotype. Efforts to develop new varieties characterized by higher yield and better wood quality will greatly benefit from recognizing and understanding the complex transcriptional network underlying wood development. The present study provides a detailed comparative description of the changes that occur in genes transcription and the biosynthesis of cell-wall-related compounds during xylogenesis in Populus trichocarpa pioneer roots and stems. Even though results of microarray analysis indicated that only approximately 10% of the differentially expressed genes were common to both organs, many fundamental mechanisms were similar; e.g. the pattern of expression of genes involved in the biosynthesis of cell wall proteins, polysaccharides, and lignins. Gas chromatography time-of-flight mass spectrometry (GC-TOF-MS) shows that the composition of monosaccharides was also very similar, with an increasing amount of xylose building secondary cell wall hemicellulose and pectins, especially in the stems. While hemicellulose degradation was typical for stems, possibly due to the intensive level of cell wall lignification. Notably, the main component of lignins in roots were guiacyl units, while syringyl units were dominant in stems, where fibers are especially needed for support. Our study is the first comprehensive analysis, at the structural and molecular level, of xylogenesis in under- and aboveground tree parts, and clearly reveals the great complexity of molecular mechanisms underlying cell wall formation and modification during xylogenesis in different plant organs.

From the Soft to the Hard: Changes in Microchemistry During Cell Wall Maturation of Walnut Shells

“…Using pectin sensitive antibodies the absence of pectin in the secondary cell wall has been verified in pine xylem (Hafren et al, 2000) and stone cells of Norway spruce phloem (Kim and Daniel, 2017). In a very recent study on xylem cell wall formation in pioneer roots and stems of poplar pectins did not colocalize in lignified cell walls, but were found in primary tissues (Marzec-Schmidt et al, 2019). The role of acidic pectin in secondary cell wall formation of the nutshell is confirmed by our intense pectin band at 853-854 cm −1 in the July sample ( Figures 4F, 6D,E), which corresponds exactly to the same position as Polygalacturonic acid (Synytsya et al, 2003).…”

Allies or Enemies: The Role of Reactive Oxygen Species in Developmental Processes of Black Cottonwood (Populus trichocarpa)

“…While the role of ROS and antioxidants in the lignification of tracheary elements in cell cultures and their role in xylogenesis in developing stems are well known, information is lacking on their role in developmental processes in underground organs, such as pioneer roots. Only a few recent studies have compared pioneer root development to the ontogeny of stems [31,32]. In these studies, similarities were noted in cell wall development and the PCD of xylem cells, as well as organ-specific mechanisms.…”

“…The increased expression of this gene, which encodes a cell-wall localized protein, in isolated secondary xylem (SX) cells from stems, indicates that RCI3 may also be involved in PCD or/and lignification of xylem cells in Populus trichocarpa during xylogenesis. Our previous study [32] demonstrated that the expression of genes encoding enzymes involved in lignification increased during stem development and grouped in Cluster II. Similar results for all genes encoding PXs were obtained in the present study.…”

“…The complete microarray dataset was submitted to the Gene Expression Omnibus database (accession number GSE126842 and GSE143559). All steps of the microarray data analysis were performed as previously described by Marzec-Schmidt et al [32].…”

“…Among the 56,055 targets present on the poplar microarray, 1171 targets were found to be differentially regulated in stems and 1914 in pioneer roots (one-way ANOVA, p ≤ 0.001, fold change ≥ 2). A detailed analysis of the results was previously described by Marzec-Schmidt et al [32]. Transcripts isolated from two stages of senescing leaves and fine absorptive roots were also profiled to catalog gene expression during the process of senescence.…”