**5. Conclusions**

In this study, we identified a total of 21 *LiNAC* genes from the transcriptome data of *L. indica*. We analyzed the physicochemical properties of the 21 LiNAC proteins and all *LiNAC* genes were localized in the nucleus, and *LiNAC7* and *LiNAC16* also had a transmembrane structure at the C-terminus. Amino acid sequence alignment showed that almost all *LiNAC* genes contain a conserved NAM structure, consisting of five substructures, A, B, C, D, and E. The phylogenetic tree constructed with *A. thaliana* classified LiNAC proteins into 2 groups and 14 subgroups. GO and KEGG enrichment analysis also indicated that *LiNAC* genes are involved in plant growth development and metabolic pathways. The lignin content in the branches of upright *L. indica* 'Shaoguifei' and weeping *L. indica* 'Xiariwuniang' were also measured and it was found that the lignin content in the two branches differed at different growth and development stages. The qRT-PCR analysis showed that the expression of *LiNAC13* and *LiNAC8* in 'Shaoguifei' was always higher than that in 'Xiariwuniang' during S1–S3, while the relative expression of *LiNAC2* in 'Shaoguifei' was lower than that in 'Xiariwuniang' in S1–S3, which indicated that *LiNAC2*, *LiNAC13*, and *LiNAC8* might regulate the weeping traits of *L. indica* through their respective regulatory pathways. However, the specific molecular mechanism of regulation and the downstream genes that jointly regulate the weeping traits need to be further verified. In conclusion, the current study improved our understanding of the role of the *NAC* gene family in weeping traits in *L. indica*.

**Supplementary Materials:** The following supporting information can be downloaded at: https://www. mdpi.com/article/10.3390/plants11162168/s1, Figure S1: The transmembrane structure of *LiNAC7* and *LiNAC16*; Figure S2: Conserved motifs in five subdomains of *LiNACs*; Table S1: Specific primers for RT-PCR of *LiNAC* in this study.

**Author Contributions:** Conceptualization, L.Y., C.G. and L.S.; methodology, C.G.; software, L.S.; validation, Q.W., Y.Z. and G.Z.; investigation, C.G. and S.H.; data curation, L.S. and Q.M.; writing original draft preparation, C.G. and L.S.; writing—review and editing, L.Y., C.G., L.S., Q.W. and G.Z.; funding acquisition, L.Y. and C.G. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was financially supported by the Research Development Fund of Zhejiang A&F University (2019FR028); Open Fund of Zhejiang Provincial Key Laboratory of Germplasm Innovation and Utilization for Garden Plants (2020E10013-K202104); Zhejiang Provincial Natural Science Foundation of China (No. LY21C160001); and Zhejiang Science and Technology Major Program on Agricultural New Variety Breeding (No. 2021C02071-4).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** All data in this study can be found in the manuscript or in the Supplementary Materials.

**Conflicts of Interest:** The authors declare no conflict of interest.
