Phospholipid signaling is an important component in eukaryotic signal transduction pathways; in plants, it plays a key role in growth and development as well as in responses to environmental stress. We cloned and characterized a gene from rice encoding phosphoinositide-specific phospholipase C (OsPI-PLC1, Oryza sativa L. phosphoinositide-specific phospholipase C1). OsPI-PLC1 encodes a 599 amino acid protein containing the catalytic X and Y domains, as well as a C2-1ike domain, characteristics of this class of enzymes. Expression of OsPI-PLC1 was induced by various chemical and biological inducers of plant defence pathways, including benzothiadiazole (BTH), salicylic acid (SA), dichloroisonicotinic acid, probenazole (PB), jasmonic acid (JA) and its methyl ester, Pseudomonas syringae pv. syringae, and wounding. All of these treatments were shown to induce resistance in rice against blast disease caused by Magrzaporthe grisea. OsPI-PLC1 was activated within 6 h after inoculation with the blast fungus in BTH-treated rice seedlings and in the incompatible interaction between a resistant genotype of rice and M. grisea, whereas the expression in the BTH-untreated seedlings and in the compatible interaction was only induced to a relatively low level at later time points (30h) after inoculation, indicating that expression of OsPI-PLC1 is associated with the resistance response and/or the incompatible interaction. In addition, BTH treatment also induced systemic expression of OsPI-PLC1. These results suggest that OsPI-PLC1 may be involved in the signaling pathways leading to disease resistance in rice.

In the present study, we cloned and identified a fulllength cDNA of a rice gene, OsBIHD1, encoding a homeodomain type transcriptional factor. OsBIHD1 is predicted to encode a 642 amino acid protein and the deduced protein sequence of OsBIHD1 contains all conserved domains, a homeodomain, a BELL domain, a SKY box, and a VSLTLGL box, which are characteristics of the BELL type homedomain proteins. The recombinant OsBIHD1 protein expressed in Escherichia coil bound to the TGTCA motif that is the characteristic c/s-element D NA sequence of the homeodomain transcriptional factors. Subcellular localization analysis revealed that the OsBIHD1 protein localized in the nucleus of the plant cells. The OsBIHD1 gene was mapped to chromosome 3 of the rice genome and is a single-copy gene with four exons and three introns. Northern blot analysis showed that expression of OsBIHD1 was activated upon treatment with benzothiadiazole (BTH), which is capable of inducing disease resistance. Expression of OsBIHD1 was also up-regulated rapidly during the first 6 h after inoculation with Magnaporthe grisea in BTH-treated rice seedlings and during the incompatible interaction between M. grisea and a resistant genotype. These results suggest that OsBIHD1 is a BELL type of homeodomain transcription factor present in the nucleus, whose induction is associated with resistance response in rice.