The seed-specific transcription factor VP1 (OSVP1) is expressed in rice suspension-cultured cells

A seed-specific transcriptional regulator, VP1, is required for the induction of ABA-regulated genes that include Lea (late embryogenesis abundant protein) genes. Although the induction of one rice Lea gene, Osem, by ABA is normally restricted to seed tissues, we found that the expression was strongly induced by ABA in the Oc line of rice suspension-cultured cells. Since this observation suggested that rice VP1 (OSVP1) protein or a functionally similar protein might be expressed in the cultured cells, we analyzed the expression of Osvp1 in these cells at both the mRNA and the protein level, we detected Osvp1 mRNA and OSVP1 protein in the cultured cells at levels similar to or higher than those in developing embryos. In the cultured cells, neither the level of total cellular OSVP1 nor that of nuclear OSVP1 protein was affected by ABA. Based on the results, the mechanism for the transcriptional regulation of VP1-dependent ABA-inducible genes is discussed.