Homeobox leucine zipper proteins and cotton improvement

Transcription factors play key roles in plant develop- ment and stress responses through their interaction with cis-elements and/or other transcription factors. Homeodomain associated leucine zipper proteins (HD-Zip) constitute a family of transcription factors that are characterized by the presence of a DNA- binding domain closely linked with leucine zipper motif functioning in dimer formation. This type of association is unique to plants and considered as an excellent candidate to activate developmental respons- es to altering environmental conditions. Cotton is the most important fiber plant with a lot of local and commercial uses in the world. HD-Zip proteins not only have key roles in different stages of vascular and inter-fascicular fiber differentiation of cotton but also are suggested to have an important role against abio- tic stress that is one of the key factors limiting cotton productivity. Plants have developed various strategies to manage stress conditions through a combination of metabolic, physiological and morphological adapta- tions. These adaptive changes rely largely on altera- tions in gene expression. Therefore, transcriptional regulators play a crucial role in stress tolerance. Be- ing a transcription factor HD-Zip might be a useful target for genetic engineering to generate multiple stress tolerance in susceptible plants. In the following chapter, we discussed how the HD-Zip proteins would play a useful role for cotton development both in fiber production and stress adaptation.