An HD-Zip transcription factor ArHDZ22 regulates plant height and decreases salt tolerance in Anoectochilus roxburghii

Salt stress seriously inhibits plants growth and crops yield. It is considered one of the key factors affecting survival of Anoectochilus roxburghii . The homeodomain leucine zipper (HD-Zip) transcription factors play vital roles in plant growth, development and response to abiotic stress. However, the function and mechanism by which they affect the salt tolerance in A. roxburghii remains unclear. In this study, we identified an HD-Zip transcription factor ArHDZ22 that is significantly induced by salt stress and belongs to the HD-Zip III subfamily derived from A. roxburghii . ArHDZ22 is highly expressed in the root of A. roxburghii , exhibiting nuclear localisation and transcriptional activity. The root growth and the maximal photochemical efficiency (Fv/Fm) values of transgenic plants overexpressing ArHDZ22 were significantly lower than those of WT plants under salt stress induction. Under normal conditions, ArHDZ22 overexpressed transgenic plants flowered early, however, which plant height was significantly lower than that of WT plants. Moreover, the expression levels of EXPANSIN11 ( EXP11 ), EXPANSIN8 ( EXP8 ), GA20-oxidases ( GA20ox1 ) were down-regulated in Arabidopsis thaliana and A. roxburghii overexpressing ArHDZ22. Combing with promoter analysis, the result implied that ArHDZ22 may regulate growth related genes by binding to HDZB-elements. Gene expression and transgenic phenotype analyses showed that ArHDZ22 negatively regulates the growth and salt tolerance of A. roxburghii . Overall, our findings provide insight into the mechanism underlying ArHDZ22-mediated salt tolerance and plant growth. • ArHDZ22 is localized in the nucleus and has transcriptional activity. • ArHDZ22 negatively regulated the salt tolerance of A. roxburghii . • ArHDZ22 shortened the flowering time of Arabidopsis and inhibited plant height. • ArHDZ22 regulates the expression of A. roxburghii elongation-related genes.