Transcriptional and temporal response of Populus stems to gravi‐stimulation

Abstract

Plants modify development in response to external stimuli, to produce new growth that is appropriate for environmental conditions. For example, gravi-stimulation of leaning branches in angiosperm trees results in modifications of wood development, to produce tension wood that pulls leaning stems upright. Here, we use gravi-stimulation and tension wood response to dissect the temporal changes in gene expression underlying wood formation in Populus stems. Using time-series analysis of seven time points over a 14-d experiment, we identified 8,919 genes that were differentially expressed between tension wood (upper) and opposite wood (lower) sides of leaning stems. Clustering of differentially expressed genes showed four major transcriptional responses, including gene clusters whose transcript levels were associated with two types of tissue-specific impulse responses that peaked at about 24-48 h, and gene clusters with sustained changes in transcript levels that persisted until the end of the 14-d experiment. Functional enrichment analysis of those clusters suggests they reflect temporal changes in pathways associated with hormone regulation, protein localization, cell wall biosynthesis and epigenetic processes. Time-series analysis of gene expression is an underutilized approach for dissecting complex developmental responses in plants, and can reveal gene clusters and mechanisms influencing development.

Brassinosteroid regulation of wood formation in poplar

“…The gravitropic response and tension wood have been used as a model system for wood development, as a dramatic change in wood anatomy and biochemistry can be experimentally manipulated through a simple and easily applied stimulus. The tension wood response is accompanied by a large change in gene expression, both in the tension wood side of the stem but also in the ‘opposite wood’ side of the stem facing the ground (Gerttula et al ., ; Zinkgraff et al ., ), supporting the notion that transcription is a key point of regulation for wood development.…”

Genome-wide analysis of the Catalpa bungei caffeic acid O-methyltransferase (COMT) gene family: identification and expression profiles in normal, tension, and opposite wood

“…Previous studies have demonstrated that tension wood (TW) and opposite wood (OW) developed under tension or compression stress generally possess physical properties that differ from those of normal wood (NW), possibly due to differences in the composition and structure of polymers that comprised of the cell wall (Chen, Chen & Zhang, 2015). Tension wood usually forms on the upper side of the bent stems and was induced by gravistimulation and has been used as a model system for the study of carbon partitioning between lignin and cellulose in trees (Zinkgraf et al, 2018). Compared to NW, TW usually has less lignin, mannose and xylose, but more glucose and cellulose (Guedes et al, 2017).…”

The Cytoskeleton and Its Role in Determining Cellulose Microfibril Angle in Secondary Cell Walls of Woody Tree Species

“…TW, developed on the upper side of angiosperms branches, is characterised by extremely low MFA values and this is often associated with upregulation of many of cytoskeleton component and secondary wall formation genes, including those listed previously [41,101,[104][105][106][108][109][110][111][112]. Accordingly, Li et al [113] found the same genes overexpressed in high stiffness wood in Pinus radiata, which also has lower MFA when compared to low stiffness wood.…”