Molecular evolution of the bZIP family in allotetraploid Gossypium and GhbZIP017 function under drought stress.

Key message: 203 bZIP members were identified in each G. barbadence and G. hirsutum and GhbZIP017 from the A subfamily was a novel drought-related member in cotton. The basic leucine zipper (bZIP) transcription factors are widely distributed in plants, but the evolutionary history is still unclear in allotetraploid Gossypium barbadense and Gossypium hirsutum. In this study, 203 bZIP members were identified in each G. barbadense and G. hirsutum. The bZIP members could be further divided into 13 subfamilies. A total of 227 gene duplication events were discovered in two allotetraploid cotton species and mainly occurred in the cotton ancestor. Furthermore, the bZIP family had a conserved evolutionary history in two allotetraploid cotton species. Meanwhile, the bZIP members had tissue-specific expression levels. Moreover, through the RNA-seq analysis, GhbZIP017 from the A subfamily played an important role in drought stress response. GhbZIP017 was localized in the nucleus and acted as a transcriptional repressor. The expression levels of GhbZIP017 in leaves and roots could be highly induced by drought stress. GhbZIP017 overexpression in Arabidopsis could enhance drought tolerance with a higher survival rate, lower membrane ion leakage, higher SOD and POD activity, lower MDA content, and higher expression levels of some drought-related genes. Overall, these results could help us uncover the evolutionary history of the bZIP members in cotton and provide a candidate gene GhbZIP017 for drought breeding in G. hirsutum.