Eukaryotic translation initiation factor 5 A (eIF5A) is the only cellular protein known to contain the unusual amino acid hypusine. However, the precise cellular function of eIF5A is to date unknown. In the present study, we report on the characterization of two cDNA clones encoding eIF5A in rice (Oryza sativa). Sequence analysis revealed that the two cDNAs share 93% amino acid sequence identity. Phylogenetic analysis of the eIF5A genes revealed paraphyly of OseIF5A-1 and OseIF5A-2. Analysis at the mRNA level has shown that OseIF5A-1 and OseIF5A-2 are expressed in rice leaves and panicles and high relative amounts of both genes were detected in old leaves. In addition, both OseIF5A-1 and OseIF5A-2 were spatially regulated during rice leaf development. In suspension-cultured cells, the transcripts of OseIF5A genes were strongly reduced after sugar starvation. Abiotic stresses, salt and heavy metal, induce the accumulation of OseIF5A-1 and OseIF5A-2 mRNAs in rice cells. These results suggested that both OseIF5A genes might be regulated by plant development and environmental stresses.

Signaling pathways, specifically calcium and calcium-dependent protein kinase (CDPK), have been implicated in the regulation of stress and developmental signals in plants. Here, we reported the isolation and characterization of an orchid, Phalaenopsis amabilis, CDPK gene, PaCDPK1, by using the rapid amplification of cDNA ends (RACE)-PCR technique. The full length cDNA of 2,310 bp contained an open reading frame for PaCDPK1 consisting of 593 amino acid residues. Sequence alignment indicated that PaCDPK1 shared similarities with other plant CDPKs. PaCDPK1 transcripts were expressed strongly in labellum but not in leaves and roots. In addition, the PaCDPK1 gene was transcriptionally activated in response to low temperature, wounding, and pathogen infection. To identify the regulatory role of the PaCDPK1 promoter, a construct containing the PaCDPK1 promoter fused to a beta-glucuronidase (GUS) gene was transferred into Arabidopsis by Agrobacterium-mediated transformation. GUS staining revealed that PaCDPK1/GUS expression was induced by cold, wounding, and pathogen challenge in leaves and stems of transgenic Arabidopsis. These results suggested that this PaCDPK1 gene promoter could be used as an endogenous promoter for biotechnological purposes in orchids.

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