Abstract
Taiwania (Taiwania cryptomerioides) is an important tree species in Taiwan because of the excellent properties of its wood and fascinating color qualities of its heartwood (HW), as well as the bioactive compounds therein. However, limited information is available as to the HW formation of this species. The objective of this research is to analyze the differentially expressed genes (DEGs) during the HW formation process from specific Taiwania xylem tissues, and to obtain genes that might be closely associated with this process. The results indicated that our analyses have captured DEGs representative to the HW formation process of Taiwania. DEGs related to the terpenoid biosynthesis pathway were all up-regulated in the transition zone (TZ) to support the biosynthesis and accumulation of terpenoids. Many DEGs related to lignin biosynthesis, and two DEGs related to pinoresinol reductase (PrR)/pinoresinol lariciresinol reductase (PLR), were up-regulated in TZ. These DEGs together are likely involved in providing the precursors for the subsequent lignan biosynthesis. Several transcription factor-, nuclease-, and protease-encoding DEGs were also highly expressed in TZ, and these DEGs might be involved in the regulation of secondary metabolite biosynthesis and the autolysis of the cellular components of ray parenchyma cells in TZ. These results provide further insights into the process of HW formation in Taiwania.
Highlights
Wood formation in trees develops from five major steps, including cell division, cell expansion, cell wall thickening, programmed cell death, and heartwood (HW) formation [1]
The results show that differentially expressed genes (DEGs) related to terpenoid, phenylpropanoid, and lignan biosynthesis pathways are up-regulated in transition zone (TZ) to support the biosynthesis and accumulation of terpenoids and lignans into Taiwania HW
For all three trees, the living ray parenchyma cells were only distributed in SW (SW-1, SW-2) and TZ, and this phenomenon was accompanied with the gradual accumulation of extractives and bioactive compounds from TZ toward HW region
Summary
Wood formation in trees develops from five major steps, including cell division, cell expansion, cell wall thickening, programmed cell death, and heartwood (HW) formation [1]. The first four steps proceed from several cell layers around the cambium region of a tree stem, whereas HW formation usually occurs a couple of annual rings away from the cambium region. The HW formation process may accumulate substantial amounts of secondary metabolites (extractives) into cell lumens or tissues. This process normally produces inner darker-colored HW, often recognizable from the paler outer SW. These extractives often render HW its natural durability, esthetic characteristics, pharmaceutical applications, and commercial value [3]
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