The procambium is made up of stem cells that give rise to various vascular cells in plants. To understand the molecular nature of procambium cells, we tried to identify genes that characterize procambium cells using Arabidopsis gene trap lines. Among 26,000 gene trap lines, we found 67 lines in which b-glucuronidase (GUS) staining occurred along vascular tissues in cotyledons and/or adult leaves. Although four gene trap lines showed procambium-preferential GUS expression, their expression

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... ns differed from each other during procambium development in root tips and young rosette leaves. Genomic regions flanking the gene trap insertion points in 25 of the 67 lines were determined, including three lines showing preferential GUS staining of the procambium. The three procambium-related genes encoded PINHEAD, katanin and an unknown DUF740 domaincontaining protein. We discuss procambium development based on the functions and the differential GUS staining patterns of the procambium-related genes.