Analysis of castor bean ribosome-inactivating proteins and their gene expression during seed development

Guilherme Loss-Morais,Andreia Carina Turchetto-Zolet,Ana Paula Körbes,Márcia Margis-Pinheiro,Alexandro Cagliari,Felipe Dos Santos Maraschin,Matheus Etges,Rogério Margis

doi:10.1590/s1415-47572013005000005

Guilherme Loss-Morais, Andreia Carina Turchetto-Zolet + Show 6 more

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https://doi.org/10.1590/s1415-47572013005000005

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Abstract

Ribosome-inactivating proteins (RIPs) are enzymes that inhibit protein synthesis after depurination of a specific adenine in rRNA. The RIP family members are classified as type I RIPs that contain an RNA-N-glycosidase domain and type II RIPs that contain a lectin domain (B chain) in addition to the glycosidase domain (A chain). In this work, we identified 30 new plant RIPs and characterized 18 Ricinus communis RIPs. Phylogenetic and functional divergence analyses indicated that the emergence of type I and II RIPs probably occurred before the monocot/eudicot split. We also report the expression profiles of 18 castor bean genes, including those for ricin and agglutinin, in five seed stages as assessed by quantitative PCR. Ricin and agglutinin were the most expressed RIPs in developing seeds although eight other RIPs were also expressed. All of the RIP genes were most highly expressed in the stages in which the endosperm was fully expanded. Although the reason for the large expansion of RIP genes in castor beans remains to be established, the differential expression patterns of the type I and type II members reinforce the existence of biological functions other than defense against predators and herbivory.

Highlights

Ribosome-inactivating proteins (RIPs) are enzymes that irreversibly inhibit protein synthesis by cleaving the glycosidic bond between adenine and ribose in the exposed loop of 28S rRNA that is involved in the interaction between rRNA and elongation factors 1 and 2, i.e., RIPs act as specific RNA-N-glycosidases (Endo and Tsurugi, 1987)
The type II R. communis RIPs Rco_Ric, Rco_Aggl, Rco_II4, Rco_II5, Rco_II6 and Rco_II11 showed the highest expression in stages S3 and S4 (Figure 6B). Together these results indicate that the 18 R. communis RIPs that were identified in silico are present in the R. communis genome and that four type I and six type II RIP genes are expressed during seed development
A systematic search in the public Phytozome and NCBI databases resulted in the identification of 84 putative ribosome-inactivation proteins (RIPs), 18 of which occurred in castor bean

Summary

Introduction

Ribosome-inactivating proteins (RIPs) are enzymes that irreversibly inhibit protein synthesis by cleaving the glycosidic bond between adenine and ribose in the exposed loop of 28S rRNA that is involved in the interaction between rRNA and elongation factors 1 and 2, i.e., RIPs act as specific RNA-N-glycosidases (Endo and Tsurugi, 1987). This specific depurination of rRNA blocks the interaction between rRNA and elongation factors and interrupts protein synthesis (Endo et al, 1991). The interest in ricin is related to its cytotoxicity towards mammalian cells (Spivak and Hendrickson, 2005), its potential use in biological weapons (Franz et al, 1997), its use as a research tool to study intracellular transport (Roberts and Smith, 2004) and its therapeutic uses against tumors (Schnell et al, 1996; Wang et al, 1998) and AIDS (Scadden et al, 1998; Donayre Torres et al, 2009)

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