title: Nectarin I is a novel, soluble germin-like protein expressed in the nectar of Nicotiana sp.
abstract: We have identified a limited number of proteins secreted into the nectar of tobacco plants. Nectarin I is the most highly expressed nectar protein and has a monomer molecular mass of 29 kDa. The other major nectar proteins are expressed at lower levels and have monomer molecular masses of 41, 54, and 65 kDa respectively. Nectarin I was purified and antiserum was raised against the protein. Under nondenaturing conditions, Nectarin I has an apparent molecular mass of > 120 kDa. The expression of Nectarin I was restricted to nectary tissues and to a much lower level in the ovary. No Nectarin I was found in petals, stems, leaves, or roots or other floral tissues. The expression of Nectarin I was also developmentally regulated. It is expressed in nectary tissues only while nectar is being actively secreted. Subsequently, the N-terminus of purified Nectarin I was sequenced. Sequence identity showed Nectarin I is related to wheat germin. Although hydrogen peroxide is readily detectable in tobacco floral nectar, we were unable to demonstrate any oxalate oxidase activity for Nectarin I. A partial cDNA encoding the mature Nectarin I N-terminus was isolated and used to probe a Nicotiana plumbaginifolia genomic library. The Nectarin I gene was isolated and the translated sequence was consistent with both N-terminal and internal cyanogen bromide-derived amino acid sequence. The gene contains a single 386 nt intron and encodes a mature protein of 197 amino acids.
authors.affiliation: Department of Biochemistry and Biophysics, Iowa State University, Ames 50011, USA.
authors.forename: C
authors.initials: C
authors.lastname: Carter
authors.forename: R A
authors.initials: RA
authors.lastname: Graham
authors.forename: R W
authors.initials: RW
authors.lastname: Thornburg
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D018744:DNA, Plant; D018506:Gene Expression Regulation, Plant; D006023:Glycoproteins / Q000145:classification / Q000235:genetics*; D008969:Molecular Sequence Data; D010802:Phylogeny; D010940:Plant Proteins / Q000145:classification / Q000235:genetics* / Q000378:metabolism; D010947:Plants, Toxic; D017386:Sequence Homology, Amino Acid; D012995:Solubility; D014026:Nicotiana / Q000254:growth & development
chemical_list: D018744:DNA, Plant; D006023:Glycoproteins; D010940:Plant Proteins; C058814:germin