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: Homeobox (HB) genes play critical roles in regulating various aspects of plant growth and development. However, little is known about HB genes in bamboo. In this study, a total of 115 HB genes ( PeHB001 ‒ PeHB115 ) were identified from moso bamboo ( Phyllostachys edulis ) and grouped into 13 distinct classes (BEL, DDT, HD-ZIP I‒IV, KNOX, NDX, PHD, PINTOX, PLINC, SAWADEE, and WOX) based on the conserved domains and phylogenetic analysis. The number of members in the different classes ranged from 2 to 24, and they usually varied in terms of exon‒intron distribution pattern and length. There were 20 conserved motifs found in 115 PeHBs, with motif 1 being the most common. Gene ontology (GO) analysis showed that PeHB s had diverse molecular functions, with 19 PeHB s being annotated as having xylem development, xylem, and phloem pattern formation functions. Co-expression network analysis showed that 10 of the 19 PeHB s had co-expression correlations, and three members of the KNOX class were hub proteins that interacted with other transcription factors (TFs) such as MYB, bHLH, and OVATE, which were associated with lignin synthesis. Yeast two-hybridization results further proved that PeHB037 (BEL class) interacted with PeHB057 (KNOX class). Transcriptome expression profiling indicated that all PeHB s except PeHB017 were expressed in at least one of the seven tissues of moso bamboo, and 90 PeHB s were expressed in all the tissues. The qRT-PCR results of the 19 PeHB s showed that most of them were upregulated in shoots as the height increased. Moreover, a KNOX binding site was found in the promoters of the key genes involved in lignin synthesis such as Pe4CL , PeC3H, PeCCR , and PeCOMT, which had positive expression correlations with five KNOX genes. Similar results were found in winter bamboo shoots with prolonged storage time, which was consistent with the degree of lignification. These results provide basic data on PeHB s in moso bamboo, which will be helpful for future functional research on PeHB s with positive regulatory roles in the process of lignification.

NAC (NAM, ATAF, and CUC) transcription factors (TFs) are implicated in the transcriptional regulation of diverse processes and have been characterized in a number of plant species. However, NAC TFs are still not well understood in bamboo, especially their potential association with the secondary cell wall (SCW). Here, 94 PeNAC s were identified and characterized in moso bamboo ( Phyllostachys edulis ). Based on their gene structures and conserved motifs, the PeNACs were divided into 11 groups according to their homologs in Arabidopsis . PeNAC s were expressed variously in different tissues of moso bamboo, suggesting their functional diversity. Fifteen PeNAC s associated with the SCW were selected for co-expression analysis and validation. It was predicted that 396 genes were co-expressed with the 15 PeNAC s, in which 16 and 55 genes were involved in the lignin catabolic process and cellulose biosynthetic process respectively. As the degree of lignification in the growing bamboo shoots increased, all 15 PeNAC s were upregulated with a trend of rising first and then decreasing except PeNAC37 , which increased continuously. These results indicated that these PeNAC s might play important roles in SCW biosynthesis and lignification in bamboo shoots. Seven of 15 PeNAC s had been found positively co-expressed with seven PeMYB s, and they had similar expression patterns with those of the PeMYB s in bamboo shoots. The targeted sites of miR164 were found in 16 PeNAC s, of which three PeNAC s associated with SCW were validated to have an opposite expression trend to that of miR164 in growing bamboo shoots. In addition, three PeNAC s were selected and verified to have self-activation activities. These results provide comprehensive information of the NAC gene family in moso bamboo, which will be helpful for further functional studies of PeNAC s to reveal the molecular regulatory mechanisms of bamboo wood property., Competing Interests: The authors declare no conflict of interest. The funding sponsors contributed reagents/materials/analysis tools in this paper.