Figure 8.

Norway spruce PaMC5, BFN, XCP, and CEP are strong candidate genes for executors of tracheid cell death. A, Hierarchical clustering of genes putatively related to PCD selected based on phylogenetic analyses. The genes that were differentially expressed (adjusted P < 0.01) during the appearance of dead earlywood cells (time point marked with the red arrow) are written in boldface. The cluster containing homologs for Arabidopsis MC9, BFN1, and XCP genes is marked with the blue rectangle next to the heat map. Sampling months are marked by colors below the heat map; green, summer; brown, autumn; blue, winter; and yellow, spring. B, Seven out of eight genes in the identified cluster were connected in the coexpression network of the spatial wood section series of the NorWood Web resource (threshold 3; http://NorWood.ConGenIE.org). PaMC5, BFN, XCP, and CEP showed the strongest correlation in their expression. The gray and red lines indicate positive and negative correlations, respectively. The width of the line is relative to the strength of the correlation. C, PaMC5, BFN, XCP, and CEP exhibited high expression in the cell death zone (red rectangle) of the tangential wood sections of NorWood.