Developmental Changes in Scots Pine Transcriptome during Heartwood Formation

Abstract

Scots pine (Pinus sylvestris L.) wood is desired in woodworking industries due to its favorable timber characteristics and natural durability that is contributed by heartwood extractives. It has been discussed whether the Scots pine heartwood extractives (mainly stilbenes and resin acids) are synthesized in the cells of the transition zone between sapwood and heartwood, or if they are transported from the sapwood. Timing of heartwood formation during the yearly cycle has also not been unambiguously defined. We measured steady-state mRNA levels in Scots pine transition zone and sapwood using RNA sequencing. Year-round expression profiles of selected transcripts were further investigated by quantitative RT-PCR. Differentially accumulating transcripts suggest that, of the Scots pine heartwood extractives, stilbenes are synthesized in situ in the transition zone and gain their carbon-skeletons from Suc and triglycerides. Resin acids, on the other hand, are synthesized early in the spring mainly in the sapwood, meaning that they must be transported to the heartwood transition zone. Heartwood formation is marked by programmed cell death that occurs during the summer months in the transition zone.

The O‐methyltransferase PMT2 mediates methylation of pinosylvin in Scots pine

“…Sapwood (SW) and transition zone (TZ) samples were collected from c . 46‐yr‐old trees (Lim et al ., ).…”

“…Samples were frozen in liquid nitrogen and stored at À80°C. Sapwood (SW) and transition zone (TZ) samples were collected from c. 46-yr-old trees (Lim et al, 2016).…”

“…From each sample point four biological replicates were sequenced. Sample processing, sequencing and mapping the reads to the Pinus EST collection (The Gene Index Databases, v.9.0), Trinity assembly of the reads and to Pinus taeda L. genome v.1.01 was done as described in Lim et al (2016). Mapped count data were used for correlation analysis to search for O-methyltransferases coexpressed with stilbene synthase.…”

“…Actin and histone genes were used as references. Primer efficiencies were tested using a mixture of cDNA from UV-C 6H and wounding 2 day samples as a template except for STS, actin and histone primers that were tested earlier (Lim et al, 2016). Amplification efficiencies were calculated using EasyqpcR R package module (Le Pape, 2015).…”

Differential responses of Scots pine stilbene synthase and chalcone synthase genes to Heterobasidion annosum infection

“…In contrast, CHS activity is present in non‐induced Scots pine plants, and its induction by stress is transient (Fliegmann et al., ). Recently, it was demonstrated that the highest level of stilbene synthase activity in Scots pine is associated with the transition zone between the sapwood and heartwood, whereas it is much lower to almost undetectable in other tissues (Lim et al., ). Furthermore, the transcription level of stilbene synthase in the transition zone shows a complex regulation pattern throughout the growing season, reaching its maximum in winter (Lim et al., ).…”