Oryza sativa PSK gene encodes a precursor of phytosulfokine- ␣ , a sulfated peptide growth

  • Yang H
  • Matsubayashi Y
  • Nakamura K
 et al. 
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Phytosulfokine- ? [PSK- , Tyr(SO3H)-Ile-Tyr(SO3H)-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- ? precursor has been isolated. The cDNA is 725 base pairs long, and the 89-aa product, preprophytosul- fokine, has a 22-aa hydrophobic region that resembles a cleavable leader peptide at its NH2 terminus. The PSK- ? sequence occurs only once within the precursor, close to the COOH terminus. [Ser4]PSK- ? 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- ? in con- ditioned 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 mRNAwasdetected at an elevated constitutive level in riceOcculture cellsonRNAblot analysis.AlthoughPSK- ? moleculeshaveneverbeen identified in any intact plant, reverse transcription–PCR analysis demonstrated that OsPSK is expressed in rice seedlings, indicating that PSK- ? 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. peptide

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  • Heping Yang

  • Yoshikatsu Matsubayashi

  • Kenzo Nakamura

  • Youji Sakagami

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