**3. Discussion**

## *3.1. The Characteristics of NAC Gene Family in L. indica*

In this study, we identified 21 complete *LiNAC* genes with Open Reading Frames based on *L. indica* transcriptome data and analyzed their basic information. We predicted and analyzed 21 LiNAC proteins, such as isoelectric power, relative molecular weight, and transmembrane structure, LiNAC7, and LiNAC16 have a transmembrane structure at the C-terminal, and it is speculated that they are likely to be NAC-membrane-binding transcription factors. Almost all *LiNAC* genes are predicted to be localized in the nucleus (Table 1); *LiNACs* are probably mostly functional in the nucleus. The conserved structure and motif of *LiNACs* were also examined (Figure 4B) and it was shown that all of them possessed the normal NAM structure (Figure 4C). Nearly all *LiNAC* genes have motif 3, motif 4, and motif 1, although motif 2 is missing from Group II, which may be related to the loss of assembled data. The motifs found in the gene members of various evolutionary branches vary and motif 3, motif 4, motif 2, motif 1, and motif 5 may be the conserved motifs in the NAC family (Figure S2). Phylogenetic trees of *L. indica* and *Arabidopsis* divide into 2 groups with 14 subgroups (Figure 1) and *LiNAC* genes were not found in many subgroups (e.g., ANAC011, ATAF, and AtNAC3/NAP). Overexpression of *AtNAP* causes early senescence in *A. thaliana* and members of the ATAF subgroup have a significant role in leaf senescence and other characteristics of plants, indicating that these subgroups may be involved in the process of plant senescence. *LiNAC8* is closely connected to AT1G32770.1, AT3G61910.1, and AT2G46770, for instance, leading one to hypothesize about the function of the *LiNAC* gene based on genetic similarities. AT1G32770.1 (*SND1*) is a key gene that regulates the synthesis of cell secondary walls. In *Arabidopsis*, *SND1* is specifically expressed in xylem fibers, and functional silencing led to secondary wall thinning and the inability of pedicel fiber cells to form secondary walls and drooping. The other subgroups of the *LiNAC* gene may play different biological functions.

Further, 18 of the 21 *LiNAC* genes were shown to be engaged in the two biological processes of GO, leaf growth and branch creation, according to KEGG and GO enrichment analyses (Figure 5). While lignin, a phenylpropane-derived polymer, together with cellulose and hemicellulose, forms the cell wall of plant vascular tissue and provides mechanical support for plant upright growth, KEGG enrichment results revealed that *LiNAC* genes were involved in the phenylpropanoid biosynthesis pathway. As a result, it is hypothesized that the *LiNAC* genes may influence the production of secondary cell walls in plants to regulate the weeping trait.
