Prediction of the Possible Role of Maize Type 3 Ribosome- Inactivating Protein in Its Root System Processing

The relative expression patterns of maize (Zea mays L.) ribosome-inactivating protein 1 (RIP1)/type 3 ribosome-inactivating protein transcript were analyzed using reverse transcription and polymerase chain reaction (RT-PCR) with template materials collected separately from mature and immature root, leaf and seed tissues. The presence of RIP transcript was only detected in mature seed and immature root tissues, but not in mature roots or leaves of test plants. The present gene expression results may not only confirm the previous suggestions with regard to the involvement of maize RIP1 in seed tissue development and germination, but also may predict the possible role of same RIP in root processing of maize plant. Introduction Ribosome-inactivating proteins (RIP) are a group of proteins with site-specific rRNA Nglycosidase activity (EC number 3.2.2.22). They specifically remove a universally conserved adenine residue from the sarcin/ricin loop of the large ribosomal RNA in both prokaryotic and eukaryotic cells (Barbieri et al. 1993, Girbes et al. 2004, Stirpe and Battelli 2006). They make susceptible ribosomes impaired in translational elongation processes and so are a group of translational inhibitors (Wool et al. 1992). These proteins are frequently found in plant species (Barbieri et al. 1993, Stirpe 2013). The first identified RIP were two potent toxins, namely ricin, from the seeds of Ricinus communis L., and abrin, from the seeds of Abrus precatorius L. (Van Damme et al. 2001). Ribosome-inactivating proteins are generally classified into two categories including type 1 and type 2 proteins. Type 1 is composed of a single chain basic proteins while type 2 RIP are heterodimers consisting of an A chain having enzymatic N-glycosidase activity and B chain/lectin with sugar binding domain (Stirpe and Battelli 2006). In some plants such as maize and barley, there are peculiar single polypeptide type 1 RIP without a lectin side chain, but are unusual in being acidic proteins until they are activated by proteolysis. These RIP are considered as type 3 RIP (Hey et al. 1995). Complex biological roles have been ascribed to RIP in different organisms, so far. They have mostly been linked to antiviral, antifungal and insecticidal defense mechanisms (Hong et al. 1996, Iglesias et al. 2005). The new understandings of the RIP enzymatic activities enhanced their diverse applications in therapeutics and medicine in human beings as well as in plant protection against pathogen attacks (Puri et al. 2012, Stirpe 2013). Ribosome-inactivating proteins have been characterized from several plant tissues such as seeds, leaves, bark and fruits (Barbieri et al. 1993, Girbes et al. 2004). However, their gene expression patterns were found to be highly differential and variable in different tissues (Bolognesi et al. 2002). Plants RIP induction has been suggested to be influenced by different developmental stages such as aging and various environmental clues such as biotic or abiotic factors (Song et al. 2000, Iglesias et al. 2008, Xu et al. 2007, Parente et al. 2008, Jiang et al. 2008). *Author for correspondence: .