Genome-wide characterization and expression analysis of the HD-Zip II gene family in response to drought and GA stresses in Nicotiana tabacum.

Background: Homeodomain-leucine ZIPper (HD-ZIP) transcription factors play crucial roles in plant growth, development, and stress responses. The HD-ZIP family is categorised into four groups (HD-ZIP I-IV). While extensive genome-wide studies have been conducted on the HD-ZIP I, III, and IV subfamily in Nicotiana tabacum (tobacco), comprehensive reports on the HD-ZIP II subfamily genes are limited.

Methods: Bioinformatics resources and tools were utilised to analyse molecular characteristics, phylogenetic homology, and protein interactions. Expression pattern analyses in various tissues and the relative expression of NtHD-ZIP II genes under drought and GA treatment were assessed by qRT-PCR.

Results: In this study, 24 HD-ZIP II members were systematically identified and categorised into seven independent clades through phylogenetic analysis involving tobacco and other plant species. We found that 19 NtHD-ZIP II genes exhibited tissue-specific expression. The transcripts of NtHD-ZIPII3, 4, 14, 23, 24 were notably induced under the drought treatments, while those of NtHD-ZIPII7, 11, 12, 20 were suppressed. Furthermore, NtHD-ZIPII15 transcripts decreased following GA treatment, whereas the transcripts of NtHD-ZIPII7, 8, 11, 12 were induced after GA treatment. Notably, an increase in trichomes was observed in tobacco leaves treated with GA and subjected to drought.

Conclusions: The expression levels of some HD-ZIP II genes were altered, and an increase in glandular trichomes was induced under GA and drought treatments in tobacco. Overall, our findings provide insights into the expression patterns of NtHD-ZIP II genes and will facilitate their functional characterisation in future studies.