Characterization of a pollen-specific and desiccation-associated AP2/ERF type transcrip tion factor gene from castor bean (Ricinus communis L.)

Abstract

DREB transcription factors (TF) belong to the super family of AP2/ERF and their involvement in protein-protein interactions and DNA binding has been proposed. AP2/ERF proteins have important functions in the transcription-al regulation of a variety of biological processes related to growth and development, as well as various responses to environmental stimuli, regulating expression of plant biotic and a biotic stress-responsive genes. In this study an AP2/ERF TF gene (named RcDREB1) was isolated from castor bean (Ricinus communis L.) and its expression was analyzed in developing seeds, leaves, ovules, stems and petals of plants cultivated under field conditions. Transcripts were only observed in pollen grains, peaking during anthesis. The RcDREB1 deduced amino acid sequence was compared to other AP2/ERF TF proteins and presented 38-78% identity. Phylogenetic analysis classified it as a member of the CBF/DREB subfamily, rooting with the subgroup A-5. The RcDREB1 promoter was fused to the gus reporter gene and used to transform tobacco. Transgenic plants were exposed to various a biotic stress treatments (low and high temperatures, drought, salinity and exogenous ABA) and no detectable GUS expression was observed, suggesting that the RcDREB1 promoter is not active under tested conditions. In silico analyses revealed the presence of three copies of the regulatory late pollen-specific element (AGAAA) in the RcDREB1 5-region. Interestingly, GUS expression was only observed in pollen grains, starting when the flower opened and initiating the senescence process; at this point, desiccated mature pollen grains are released from anthers. In addition, dehydrated developing pollen grains also expressed the gus gene. This is the first study on a DREB gene presenting pollen-specific expression. © F. Aragão et al., 2013 Licensee PAGEPress srl, Italy.