EgNRT2.3 and EgNAR2 expression are controlled by nitrogen deprivation and encode proteins that function as a two-component nitrate uptake system in oil palm.

Oil palm (Elaeis guineensis Jacq.) is an important crop for oil and biodiesel production. Oil palm plantations require extensive fertilizer additions to achieve a high yield. Fertilizer application decisions and management for oil palm farming rely on leaf tissue and soil nutrient analyses with little information available to describe the key players for nutrient uptake. A molecular understanding of how nutrients, especially nitrogen (N), are taken up in oil palm is very important to improve fertilizer use and formulation practice in oil palm plantations. In this work, two nitrate uptake genes in oil palm, EgNRT2.3 and EgNAR2, were cloned and characterized. Spatial expression analysis showed high expression of these two genes was mainly found in un-lignified young roots. Interestingly, EgNRT2.3 and EgNAR2 were up-regulated by N deprivation, but their expression pattern depended on the form of N source. Promoter analysis of these two genes confirmed the presence of regulatory elements that support these expression patterns. The Xenopus oocyte assay showed that EgNRT2.3 and EgNAR2 had to act together to take up nitrate. The results suggest that EgNRT2.3 and EgNAR2 act as a two-component nitrate uptake system in oil palm.

Molecular characterization of Galectin-8 from Nile tilapia (Oreochromis niloticus Linn.) and its response to bacterial infection.

Galectins belong to the family of galactoside-binding proteins and play a major role in the immune and inflammatory responses of vertebrates and invertebrates. The galectin family is divided into three subtypes based on molecular structure; prototypes, chimera types, and tandem-repeated types. We isolated and characterized the cDNA of galectin-8 (OnGal-8) in Nile tilapia (Oreochromis niloticus). OnGal-8 consisted of a 966 bp open reading frame (ORF) that encoded a 321 amino acid protein (43.47 kDa). Homology and phylogenetic tree analysis suggested the protein was clustered with galectin-8s from other animal species and shared at least 56.8% identity with salmon galectin-8. Structurally, the amino acid sequence included two distinct N- and C- terminus carbohydrate recognition domains (CRDs) of 135 and 133 amino acids, respectively, that were connected by a 39 amino acid polypeptide linker. The N- and C-CRDs contained two conserved WG-E-I and WG-E-T motifs, suggesting they have an important role in mediating the specific interactions between OnGal-8 and saccharide moieties such as ß-galactoside. The structure of OnGal-8 was characterized by a two-fold symmetric pattern of 10-and 12-stranded antiparallel ß-sheets of both N- and C-CRDs, and the peptide linker presumably formed a random coil similar to the characteristic tandem-repeat type galectin. The expression of OnGal-8 in healthy fish was highest in the skin, intestine, and brain. Experimental challenge of Nile tilapia with S. agalactiae resulted in significant up-regulation of OnGal-8in the spleen after 5 d. Our results suggest that OnGal-8 is involved in the immune response to bacterial infection.