Characterization of a Pollen-Specific and Desiccation-Associated AP2/ERF Type Transcription Factor Gene from Castor Bean (Ricinus communis L.)

Abstract

DREB transcription factors (TF) belong to the superfamily of AP2/ERF and their involvement in protein-protein interactions and DNA binding has been proposed. AP2/ERF proteins have important functions in the transcriptional 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 abiotic stress-responsive genes. In this study an AP2/ERF TF gene (named <em>RcDREB1</em>) was isolated from castor bean (<em>Ricinus communis L</em>.) 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 <em>RcDREB1 </em>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 <em>RcDREB1</em> promoter was fused to the gus reporter gene and used to transform tobacco. Transgenic plants were exposed to various abiotic stress treatments (low and high tempera- tures, drought, salinity and exogenous ABA) and no detectable GUS expression was observed, suggesting that the <em>RcDREB1</em> promoter is not active under tested conditions. <em>In silico</em> analyses revealed the presence of three copies of the regulatory late pollen-specific element (AGAAA) in the <em>RcDREB1</em> 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 <em>gus</em> gene. This is the first study on a <em>DREB</em> gene presenting pollen-specific expression

Expression of a DREB 5-A subgroup transcription factor gene from Ricinus communis (RcDREB1) enhanced growth, drought tolerance and pollen viability in tobacco

“…We previously isolated and characterized a DREB coding gene from castor bean (Cipriano et al 2013). Its expression was observed mainly in pollen, peaking during anthesis, with the ower opening, initiating the senescence process.…”

“…Phylogenetic analyses have rooted RcDREB1 as a member of the CBF/DREB subfamily A-5 subgroup, in which several proteins have been characterized as stress-inducible, and belonging to the ABA signaling pathway (Mizoi et al 2012;Bouaziz et al 2012;Cipriano et al 2013;Ren et al 2019). The higher aerial part/root ratios observed in transgenic lines suggest a greater allocation of photo-assimilates to the aerial parts, when compared to the non-transgenic plants.…”

“…We have isolated and characterized an AP2/ERF TF gene (named RcDREB1) from castor bean (Ricinus communis L.) coding for a protein that presented 38-78% identity when compared to other AP2/ERF TF proteins (Cipriano et al 2013). In R. communis, RcDREB1 transcripts were only observed in pollen grains, peaking during anthesis.…”

“…In R. communis, RcDREB1 transcripts were only observed in pollen grains, peaking during anthesis. Phylogenetic analysis classi ed it as a member of the CBF/DREB subfamily, rooting with subgroup A-5 (Cipriano et al, 2013). The RcDREB1 promoter was fused to the gus reporter gene and its expression observed in several tissues of transgenic tobacco plants exposed to low and high temperatures, drought, salinity and exogenous ABA (Cipriano et al 2013).…”