Characterization of a rice (Oryza sativa L.) Bowman-Birk proteinase inhibitor: tightly light regulated induction in response to cut, jasmonic acid, ethylene and protein phosphatase 2A inhibitors.

The Bowman-Birk (BB) family of proteinase inhibitors (PI), initially reported from legume seeds, and thereafter also from wounded alfalfa and maize leaves appear to be regulated in similar ways as the extensively characterized PI I and PI II family from dicots. Here, we report a first characterization of the expression profiles of a rice (Oryza sativa L. cv. Nipponbare) BBPI gene, OsBBPI, which is part of a multigene family as demonstrated by genomic Southern hybridization. OsBBPI was found to be rapidly induced in rice seedling leaf in response to cut, exogenous jasmonic acid (JA), and two potent protein phosphatase 2A (PP2A) inhibitors, cantharidin (CN) and endothall (EN), in a light/dark-, time- and dose-dependent manner; this induction was completely inhibited by cycloheximide (CHX), indicating a requirement for de novo protein synthesis in its induction. Surprisingly, dark strongly up regulated cut-, JA-, CN-, and EN-induced OsBBPI expression, with the strongest enhancement observed with JA. A simultaneous application of a serine/threonine protein kinase inhibitor staurosporine (ST) did not affect significantly the JA-, CN-, and EN-induced OsBBPI transcript. Besides JA, it was found that the ethylene generator ethephon (ET) also had an enhancing effect on OsBBPI transcript, suggesting a direct effect of ethylene on OsBBPI expression. However, a simultaneous application of salicylic acid (SA) and abscisic acid (ABA), with JA, respectively, completely blocked OsBBPI gene expression, whereas kinetin (KN) was only partially effective. To the best of our knowledge, complete inhibition of JA-induced OsBBPI expression by SA is the first report in monocots, and with ABA in plants. Taken together, these results suggest that among the phytohormones tested here, JA and ethylene play important role(s) in regulating OsBBPI expression, with an intimate interaction with light signals. Finally, that the induced OsBBPI expression follows a kinase-signaling cascade is implied by the use of PP2A inhibitors.