Abstract
Summary Plant secondary cell walls constitute the majority of plant biomass. They are predominantly found in xylem cells, which are derived from vascular initials during vascularization. Little is known about these processes in grass species despite their emerging importance as biomass feedstocks. The targeted biofuel crop Sorghum bicolor has a sequenced and well‐annotated genome, making it an ideal monocot model for addressing vascularization and biomass deposition.Here we generated tissue‐specific transcriptome and DNA methylome data from sorghum shoots, roots and developing root vascular and nonvascular tissues.Many genes associated with vascular development in other species show enriched expression in developing vasculature. However, several transcription factor families varied in vascular expression in sorghum compared with Arabidopsis and maize. Furthermore, differential expression of genes associated with DNA methylation were identified between vascular and nonvascular tissues, implying that changes in DNA methylation are a feature of sorghum root vascularization, which we confirmed using tissue‐specific DNA methylome data. Roots treated with a DNA methylation inhibitor also showed a significant decrease in root length.Tissues and organs can be discriminated based on their genomic methylation patterns and methylation context. Consequently, tissue‐specific changes in DNA methylation are part of the normal developmental process.
Highlights
Secondary cell walls (SCWs) such as those in the xylem constitute the majority of plant biomass and are an abundant source of biomaterials
Genes required for xylem cell proliferation and their subsequent differentiation are expressed in the vascular cylinder of the root meristem and elongation zone, before the deposition of the secondary cell walls in the maturation zone (Brady et al, 2007a), making the root tip an excellent system for analyzing xylem development
To ensure successful isolation of laser capture microdissection (LCM) tissues and characterization of differential expression, quantitative reverse transcription polymerase chain reaction (qRT-PCR) was performed on tissue-specific marker genes (Fig. S3)
Summary
Secondary cell walls (SCWs) such as those in the xylem constitute the majority of plant biomass and are an abundant source of biomaterials. Vascularization, or development of functional conductive tissue from undifferentiated cells, is relatively well understood in the dicot Arabidopsis thaliana, for xylem tissue (see Ruzicka et al (2015), and Kumar et al (2016) for recent reviews). Little is known about vascular specification and xylem differentiation in monocots despite their emerging importance as biomass feedstock for the emerging bioenergy industry (Somerville, 2006). Dicots contain walls comprising cellulose and xyloglucan in roughly equal amounts, present in a pectin-abundant gel. Glucoarabinoxylans are the major hemicelluloses as opposed to xyloglucan, while cell walls are pectin-poor (Carpita, 1996). The SCWs of monocots contain higher amounts of lignin and, in some cases, silica (Vogel, 2008)
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