Plants expressing murine pro-apoptotic protein Bid do not have enhanced PCD
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RESEARCH NOTE
Plants expressing murine pro‑apoptotic protein Bid do not have enhanced PCD Anna Manara* , Zahra Imanifard, Linda Fracasso, Diana Bellin and Massimo Crimi*
Abstract Objectives: The purpose of this study was to explore whether plant programmed cell death (PCD) cascade can sense the presence of the animal-only BH3 protein Bid, a BCL-2 family protein known to play a regulatory role in the signaling cascade of animal apoptosis. Results: We have expressed the mouse pro-apoptotic protein Bid in Arabidopsis thaliana and in Nicotiana tabacum. We did not obtain any transformed plant constitutively expressing the truncated protein (tBid—i.e. the caspaseactivated form) whereas ectopic expression of the full-length protein (flBid) does not interfere with growth and development of the transformed plants. To verify whether the presence of this animal pro-apoptotic protein modified stress responses and PCD execution, both N. tabacum and A. thaliana plants constitutively expressing flBid have been studied under different stress conditions triggering cell death activation. The results show that the presence of flBid in transgenic plants did not significantly change the responses to abiotic stress ( H2O2 or NO) and biotic stress treatments. Moreover, the finding that no Bid active form was present in treated tobacco plants suggests an absence of a proper activation of Bid. Keywords: Programmed cell death, Apoptosis, BH3-only protein, Bid, Oxidative stress, Nitric oxide, Plant pathogen Introduction Programmed cell death (PCD) is present both in animal and plant systems, where different modes of action have been recognized and studied. Among these, apoptosis and apoptotic-like PCD differentiate from other forms of cell death and share common morphological characteristics. In animals, apoptotic cell death involves the Bcl-2 protein family as the initiator of the signaling pathway and a cascade of caspases for the execution of the death program [1]. So far, no Bcl-2 proteins have been identified in plants. Nevertheless, there is evidence that Bcl-2-like proteins exist. In 2001, a gene encoding for a homolog of the human gene BI-1 was isolated from Arabidopsis (AtBI) [2]. The existence of a functional Bax Inhibitor in
*Correspondence: [email protected]; [email protected] Department of Biotechnology, University of Verona, Strada Le Grazie 15, 37134 Verona, Italy
plant indicated the possibility of a Bax-like mechanism in plants or the presence of a regulatory system similar to that of animals (i.e. pro- and anti-apoptotic mediators). Moreover, when the anti-apoptotic gene Bcl-XL was expressed in tobacco, death triggered by inducers of cellular ROS like UV, paraquat or TMV, was suppressed [3]. In addition, the expression of anti-apoptotic genes (BclXl and Ced-9) in tomato plants improved tolerance to viral infection and low temperature exposure [4]. These results indicated that a conserved apoptotic pathway might be present in plants with divergent proteins. In order to study the
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