[Biological functions of HD-Zip transcription factors]

The HD-Zip transcription factors, which are unique to plant kingdom, belong to Homeobox proteins. They are composed of highly conserved HD (Homeodomain) and Leu zipper (Zip) element. The former binds specifically to DNA and the later mediates the formation of dimerization. Based on the structure features, HD-Zip transcription factors can be classified into four subfamilies HD-Zip I - IV, which are involved in different biological processes of plants including growth and development, photomorphogenesis, flowering, fruit ripening, and adaptation response to environmental stresses. HD-Zip transcription factors act as the integrators of development and environmental cues and endogenous hormone signal pathway to regulate targeted gene expression and plants adaptation response. In this review, the most advanced researches on biological functions of HD-Zip were summarized based on the researches of Arabidopsis HD-Zip transcription factors and the results from other species. The aim of this article is to provide the basis for studying the functions of new genes encoding HD-Zip proteins from other species and illustrating the molecular mechanism of HD-Zip on growth and development of plant under normal and unfavorable conditions.