Functional analyses of a D-type cyclin, OsCYCD4;1, from rice potentially involved in bundle sheath formation

Abstract

Previously, a high-level expression a D-type cyclin gene was observed in transgenic rice regenerants with multiple shoots caused by overexpression of a T-DNA ipt gene. According to its sequence characteristics, the cyclin gene was classified into type D4;1 (designated as OsCYCD4;1). Though the overexpression result implied that OsCYCD4;1 is regulated by cytokinins, addition of various phytohormones including BA on rice tissues did not increase the transcripts. For more detailed analyses of OsCYCD4;1 expression, transgenic plants carrying OsCYCD4;1 promoter::gus gene were produced. GUS staining of these transgenic plants and in situ hybridization analysis showed that OsCYCD4;1 was not transcribed in meristems, but in procambium at the early stage of vascular development and also differentiated vascular bundles except xylem. Moreover, ectopic expression of OsCYCD4;1 caused disorganized vascular bundles. The results suggested a role of OsCycD4;1 in the development of vascular systems, which is different from those of typical mitotic cyclins.