Perfil transcricional da xilogênese em <i>Eucalyptus grandis</i>

Abstract

Transcriptional profile of xylogenesis in Eucalyptus grandis Eucalyptus (Eucalyptus spp.) is the most important commercial tree in Brazil, playing a significant role in the pulp and paper industry. An increase in the yield of cellulosic pulp extraction and a reduction of production cost are the main objectives of the eucalyptus breeding programs. As the delignification process is fundamental for the extraction of cellulose, it is highly important to understand the biosynthesis and deposition of the secondary cell wall during xylogenesis. The differentiation of the tracheary elements is characterized by the deposition of the secondary cell wall, so studies of gene expression involving these xylem cells is an interesting strategy. Sequencing of the transcriptome of cells in suspension at different stages of development (meristematic cells, elongated cells and tracheal elements) was performed generating 348 million paired-end reads with 100 bp each, with most readings (80%) aligned and mapped against reference genome. The analysis of differentially expressed genes (DEG) identified a total of 3426, 1044 and 4665 DEGs in the comparisons M vs. A, A vs. T and M vs. T, respectively. Being 1316, 567, 2637 up-regulated genes and 2110, 476, 2028 down-regulated genes in the M/A, T/A, T/M, respectively. A total of 4229 genes were functionally annotated and mapped in 310 routes identified by the KEGG, yielding 40 sequences related to the phenylpropanoid route, the fifth most representative route. When DEGs with log2 fold change ≤-1.5 e log2 fold change ≥ 1.5 were considered, 34 metabolic routes were identified. From these, the main route was the phenylpropanoids pathway, with 14 sequences correlated to the enzyme lactoperoxidase. The GO terms enrichment was carried out and the networks of cellulose and xyloglucans biosynthesis, ethylene signaling routes, biogenesis routes and the plant cell wall organization and cell death, among others, were highlighted. Thirty-one transcription factors were identified, being 3 MYB transcription factors, 2 NAC transcription factors and 10 WRKY transcription factors. In addition, 21, 7 and 23 genes of the cellulose and hemicelluloses pathway and 24, 8 and 21 genes of lignin monomer synthesis route were found in the M vs. A, A vs. T and M vs. T comparisons, respectively. Besides this, encoding genes laccases and peroxidases were found, participating in the polymerization of lignin monomers. The results allowed a broader understanding of the transcriptional regulation of secondary cell wall biosynthesis in eucalyptus xylem cells and revealed new genes participating in xylogenesis. This set of transcriptional data will help in the accomplishment of genetic manipulations in order to obtain eucalyptus plants with extractability characteristics aspired by the industry.