title: Oryza sativa PSK gene encodes a precursor of phytosulfokine-alpha, a sulfated peptide growth factor found in plants.
abstract: Phytosulfokine-alpha [PSK-alpha, Tyr(SO(3)H)-Ile-Tyr(SO(3)H)-Thr-Gln], a sulfated mitogenic peptide found in plants, strongly promotes proliferation of plant cells in culture at very low concentrations. Oryza sativa PSK (OsPSK) cDNA encoding a PSK-alpha precursor has been isolated. The cDNA is 725 base pairs long, and the 89-aa product, preprophytosulfokine, has a 22-aa hydrophobic region that resembles a cleavable leader peptide at its NH(2) terminus. The PSK-alpha sequence occurs only once within the precursor, close to the COOH terminus. [Ser(4)]PSK-alpha was secreted by transgenic rice Oc cells harboring a mutated OsPSK cDNA, suggesting proteolytic processing from the larger precursor, a feature commonly found in animal systems. Whereas PSK-alpha in conditioned medium with sense transgenic Oc cells was 1.6 times as concentrated as in the control case, antisense transgenic Oc cells produced less than 60% of the control level. Preprophytosulfokine mRNA was detected at an elevated constitutive level in rice Oc culture cells on RNA blot analysis. Although PSK-alpha molecules have never been identified in any intact plant, reverse transcription-PCR analysis demonstrated that OsPSK is expressed in rice seedlings, indicating that PSK-alpha may be important for plant cell proliferation both in vitro and in vivo. DNA blot analysis demonstrated that OsPSK homologs may occur in dicot as well as monocot plants.
authors.affiliation: Laboratory of Bioactive Natural Product Chemistry, Graduate School of Bio-Agricultural Sciences, Nagoya University, Chikusa, Nagoya 464-8601, Japan. hyang@agr.nagoya-u.ac.jp
authors.forename: H
authors.initials: H
authors.lastname: Yang
authors.forename: Y
authors.initials: Y
authors.lastname: Matsubayashi
authors.forename: K
authors.initials: K
authors.lastname: Nakamura
authors.forename: Y
authors.initials: Y
authors.lastname: Sakagami
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D002478:Cells, Cultured; D003001:Cloning, Molecular; D018076:DNA, Complementary; D018506:Gene Expression Regulation, Plant; D008969:Molecular Sequence Data; D012275:Oryza / Q000235:genetics*; D036361:Peptide Hormones; D010937:Plant Growth Regulators; D010940:Plant Proteins / Q000235:genetics*; D014176:Protein Biosynthesis; D011498:Protein Precursors / Q000235:genetics*; D017386:Sequence Homology, Amino Acid
chemical_list: D018076:DNA, Complementary; C400764:PSK protein, Oryza sativa; C100975:PSK-alpha protein, plant; D036361:Peptide Hormones; D010937:Plant Growth Regulators; D010940:Plant Proteins; D011498:Protein Precursors