*2.4.* D. officinale PLP\_deC *Gene Expression in Di*ff*erent Tissues*

To understand the gene expression pattern of the *PLP\_deC* genes in *D. o*ffi*cinale*, we performed an overall in silico analysis of gene expression profiles in eight tissues (root, root tip, stem, leaf, sepal, column, lip, and flower bud). These *PLP\_deC* genes exhibited distinct organ-specific expression and could be divided into three groups. As shown in Figure 4, in group A, two genes (*DoAAD1* and *DoAAD2*) were highly expressed in the flower bud and lip columns, indicating that these *PLP\_deC* genes may be involved in the development of these tissues. In addition, *DoAAD2* had a high expression level in the sepal, indicating that *DoAAD2* may be involved in sepal development. The four *PLP\_deC* genes in group B were generally expressed in low amounts in all eight tissues. Remarkably, a homologous gene pair (*DoGAD2*–*DoGAD4*) exhibited similar patterns of expression and had relatively low transcript abundance in different tissues. In group C, *DoAAD3* had low expression in all tissues. *DoGAD3* had higher expression levels in the column and sepal. Overall, the *PLP\_deC* genes with high expression levels may be involved in tissue growth and differentiation in *D. o*ffi*cinale*.

**Figure 4.** Expression profiles of *PLP\_deC* genes in different tissues. (**a**) Heatmap of the in silico expression analysis in different tissues and organs. Blue and red indicate lower and higher transcript abundance, respectively. (**b**) *PLP\_deC* genes expressed in different tissues and organs. Green, yellow, and red indicate low (0.01–0.71 FPKM), medium (1–1.71 FPKM), and high (3.42–28.4 FPKM) expression, respectively.
