Cloning and characterization of a novel transcript encoding a rna-binding protein from oil palm (Elaeis guineensis jacq.)

RNA-binding proteins (RBPs) have been implicated as regulatory proteins involved in the post-transcriptional processes of gene expression in plants that influence floral development, circadian rhythms, hormone signaling, plant growth, abiotic stress response and tolerance. RBPs have received much attention in Arabidopsis, tobacco and rice. Oil palm (Elaeis guineensis Jacq.) is the most efficient oil-yielding crop in the world. Environmental stresses have a major impact on oil palm production mainly plant growth, physiology and oil yield. However, the biological functions of RBPs in post-transcription regulation of gene expression in response to stresses are still poorly understood in oil palm. This study aimed to understand the regulation of target transcripts by a RBP from oil palm at post-transcriptional level, the regulatory factors associated with the target RBP in the ribonucleoprotein complex and the involvement of RBP in post-transcriptional RNA mechanism in response to environmental stimuli in oil palm. In this study, a gene designated as EgRBP42, encoding a plant heterogeneous nuclear ribonucleoprotein-like RBP was isolated from oil palm. EgRBP42 was identified from an expressed sequence tag (EL684239) from the oil palm female inflorescence. EgRBP42 protein consists of two N-terminal RNA recognition motifs and a glycine-rich domain at the C-terminus. The upstream region of EgRBP42 has multiple light-responsive, stress-responsive and flower development related regulatory elements. Real-time RT-PCR analysis showed that EgRBP42 was expressed in all oil palm tissues tested, including leaf, shoot apical meristem, root, female inflorescence, male inflorescence and mesocarp with the lowest transcript level in the roots. EgRBP42 protein interacted with transcripts associated with stress responses, transcription and translation. Validation of consensus sequence of interactive transcripts binding to EgRBP42 indicated that EgRBP42 binds to the AG-rich region on its interactive transcripts. Three variants of EgRBP42 at the 3’-untranslated regions were detected from oil palm leaf tissue. The accumulation of EgRBP42, its interacting transcripts and its alternative 3’-UTR variant transcripts were up-regulated (> 2 fold change) by abiotic stresses, including salinity, drought, submergence, cold and heat stresses in leaf discs (short-term stress treatment for 30 min to 28 hr) and leaves from oil palm seedlings (long-term stress treatment for 7 days). Coimmunoprecipitation and yeast II hybrid interaction studies showed that EgRBP42 protein interacted with various regulatory factors involved in transcription, nucleocytoplasmic transport, mRNA degradation and translation. The protein accumulation of EgRBP42 was up-regulated (> 2-fold change) by heat, cold, drought and salinity in oil palm seedlings exposed to long-term stress treatments for 7 days. Collectively, the data suggested that EgRBP42 is responsive to various abiotic stresses. It is potentially a nucleocytoplasmic transporter of stress-responsive mRNAs from nucleus to cytoplasm for their rapid translation in response to heat, cold and drought stresses. This study provided information on post-transcriptional regulatory mechanisms of EgRBP42 in oil palm. Hence, EgRBP42 may be useful for the engineering of stress tolerant oil palm.

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