Rice (Oryza sativa L.) OsPR1b gene is phytohormonally regulated in close interaction with light signals.

Strategies evolved by plants to counteract a variety of biotic/abiotic stresses include induction of genes encoding pathogenesis-related (PR) protein, in particular the PR class 1 (PR1) gene family, widely used in stress response studies. In spite of its immense importance as a PR family member, and an accepted gene marker in plant disease/defense in dicots, little is known about rice PR1 genes. Recently, we cloned and characterized the first OsPR1a (rice acidic PR1) gene (Agrawal et al. (2000) Biochem. Biophys. Res. Commun. 274, 157-165). Here, we report characterization of a rice basic PR1 (OsPR1b) gene, identified from screening a cDNA library prepared from jasmonic acid (JA)-treated rice seedling leaf, providing detailed and valuable insights into rice PR1 gene expression. The deduced amino acid sequence of OsPR1b reveals only 63.1% homology with the OsPR1a protein, whereas Southern blot analyses indicate that OsPR1b is a multigene family. The JA-inducible OsPR1b gene was also up-regulated by salicylic acid (SA), abscisic acid (ABA), and kinetin (KN). Furthermore, protein phosphatase inhibitors, cantharidin (CN) and endothall (EN) strongly induced the OsPR1b transcript. However, OsPR1b was not cut-responsive, diagrammatically opposite to cut inducibility of OsPR1a. This induction was light-, time-, and dose-dependent, as demonstrated by using, JA, CN, and EN, and completely inhibited by cycloheximide, but not by tetracycline. The simultaneous application of SA, and ABA, with JA, respectively, showed almost complete inhibition of the JA-induced OsPR1b transcript by 200 microM SA or ABA, but not by 100 microM concentrated solutions, suggesting a potential interaction among JA, SA, and ABA, whereas KN dramatically enhanced JA-induced OsPR1b transcript upon simultaneous application. Moreover, a simultaneous application of staurosporine enhances JA-, CN-, and EN-induced OsPR1b transcript, in particular with CN. Finally, a comparative analysis with the OsPR1a gene gives us insight into the differential regulation of the PR1 gene family, while proposing OsPR1 genes as important gene markers in rice, with potential use(s) in analyzing plant defense responses.