Abstract

Homeobox(HB) genes play critical roles in the regulation of plant morphogenesis, growth and development. Here, we identified a total of 156PtrHBgenes from thePopulus trichocarpagenome. According to the topologies and taxonomy of the phylogenetic tree constructed byArabidopsis thalianaHB members, all PtrHB proteins were divided into six subgroups, namely HD-ZIP, ZF-HD, HB-PHD, TALE, WOX and HB-OTHERS. Multiple alignments of conserved homeodomains (HDs) revealed the conserved loci of each subgroup, while gene structure analysis showed similar exon–intron gene structures, and motif analysis indicated the similarity of motif number and pattern in the same subgroup. Promoter analysis indicated that the promoters ofPtrHBgenes contain a series ofcis-acting regulatory elements involved in responding to various abiotic stresses, indicating thatPtrHBs had potential functions in these processes. Collinearity analysis revealed that there are 96 pairs of 127PtrHBgenes mainly distributing on Chromosomes 1, 2, and 5. We analyzed the spatio-temporal expression patterns ofPtrHBgenes, and the virus-induced gene silencing (VIGS) ofPtrHB3gene resulted in the compromised tolerance of poplar seedlings to mannitol treatment. The bioinformatics onPtrHBfamily and preliminary exploration of drought-responsive genes can provide support for further study of the family in woody plants, especially in drought-related biological processes. It also provides a direction for developing new varieties of poplar with drought resistance. Overall, our results provided significant information for further functional analysis ofPtrHBgenes in poplar and demonstrated thatPtrHB3is a dominant gene regulating tolerance to water stress treatment in poplar seedlings.Keywords:Homeobox;phylogenetic analysis;VIGS;PtrHB3;Populus