*2.4. Annotation and Enrichment Analysis of LiNAC Genes*

GO functional annotation of 21 *LiNAC* genes revealed that 18 of them are involved in biological processes (BPs), cellular components (CCs), and molecular functions (MFs). We examined the GO enrichment data of 18 *LiNAC* genes to forecast their biological roles. The immunological effector mechanism has the highest degree of enrichment, as shown in Figure 5A, scoring 54.4, followed by the response of cells to cold stress, with an enrichment score of 51.72. Additionally, we found that many genes have roles in a variety of developmental processes (such as leaf development and shoot development).

**Figure 5.** The GO terms (**A**) and KEGG pathways (**B**) enriched of *LiNAC* genes. The black circles indicate the number of target genes and different colors indicate the *p*−value.

As shown in Figure 5B, five *LiNAC* genes were enriched in the Nucleocytoplasmic Transport (ko03013), Phenylpropanoid Biosynthesis Pathway (ko00940), and Signal Pathway (ko04020), according to a KEGG pathway analysis of 21 *LiNAC* genes.

#### *2.5. Determination and Analysis of Lignin Content*

The lignin content in *L. indica* was measured by collecting the branches of 'Shaoguifei' and 'Xiariwuniang' at the early growth stage, the growth stage, and the end of the growth stage. The lignin content in the branches was analyzed separately for different stages and plants. Figure 6C shows that the lignin content in the branches of both 'Shaoguifei' and 'Xiariwuniang' increased gradually with the maturity of the growth period and the lignin content in 'Shaoguifei' was always higher than that in 'Xiariwuniang'. We found that the difference in lignin content between the two branches was not obvious at the early growth stage, but there was a significant difference between the lignin content in 'Shaoguifei' and 'Xiariwuniang' at the growth stage and the end of the growth stage.

**Figure 6.** The trait of *L. indica* 'Shaoguifei' (**A**) and *L. indica* 'Xiariwuniang' (**B**) and lignin content of the two (**C**) at different growth stages. S1, S2, and S3 indicate the early growth stage, the growth stage, and the end of the growth stage. Different letters a–f indicate statistically significant differences in expression.
