# The Class I HD-ZIP transcription factor PagHB7a functions as a positive regulator of salt tolerance in Populus

## TL;DR

This study shows that the PagHB7a gene helps poplar trees tolerate salt stress by enhancing their response to abiotic stress and ABA.

## Contribution

The study identifies PagHB7a as a novel positive regulator of salt tolerance in poplar through functional and genetic analysis.

## Key findings

- PagHB7a is significantly induced by salt and ABA treatments and regulated by PagAREB1s.
- Overexpression of PagHB7a enhances salt tolerance, while its knockout reduces it.
- Transcriptome analysis shows upregulated pathways related to salt, ABA, and oxidative stress in PagHB7a-OE plants.

## Abstract

Homeodomain leucine zipper (HD-ZIP) proteins are plant-specific transcription factors that play important roles in plant development and abiotic responses. In our previous study, the PagHB7a gene was identified, which belongs to the Class I HD ZIP family, and was among the most significantly induced genes by salt stress in poplar. In the present study, the role of PagHB7a was functionally characterized in salt stress responses. Expression analysis confirmed that PagHB7a was significantly induced by salt and abscisic acid (ABA) treatments; moreover, PagHB7a was directly regulated by the ABA-responsive element (ABRE) binding proteins (PagAREB1s). Genetic analysis showed that overexpression of PagHB7a (PagHB7a-OE) significantly enhanced salt tolerance, whereas CRISPR/Cas9-mediated knockout of PagHB7a (PagHB7a-KO) significantly reduced it. Transcriptome analysis revealed that biological pathways responding to salt stress, ABA, and oxidative stress were significantly upregulated in PagHB7a-OE plants. Collectively, our results demonstrate that PagHB7a, a salt stress- and ABA-inducible transcription factor, acts as a positive regulator of salt tolerance in Populus.