Introduction 1934 2003 2006 2006 2006 2001 Arabidopsis max1 2 3 4 rms1 2 3 4 5 dad1 2 1995 1998 2004 RB RB PCNA 1998 2003 2002 2006 2003 Zea mays 1997 1996 1996 Nicotiana tabacum 1999 Chenopodium rubrum 1999 Arabidopsis thaliana 2000 Populus tremula Populus tremuloides Cocos nucifera Oryza sativa 1997 1996 1998 1999 1999 1999 1996 1996 1998 1999 2001 2002 2004 2006 2005 Pisum sativum Materials and methods Plant growth and tissue collection Pisum sativum PCR and cloning of PsRBR1 cDNA 1993 + 6 32 1998 DNA sequencing The cDNAs were sequenced by the dideoxy chain termination method using an automatic DNA sequencer (LIC-4000, LI-COR Inc., Lincoln, NE) according to the manufacturer’s protocol. Both strands were entirely sequenced. Yeast two-hybrid system PsRBR1 Saccharomyces cerevisiae O Antibody preparation and immunoblot analysis Escherichia coli 3 4 In vitro-coupled transcription and translation PsRBR1 n 35 Dephosphorylation 2 RNA extraction and blot analysis PsRBR1 PCNA Histone H4 32 2 4 2 4 Phospholabeling and immunoprecipitation 32 Results Isolation of a pea cDNA encoding RB-related protein PsRBR1 PsRBR1 1 1997 1996 1990 Fig. 1 PsRBR1 A B  1 1 Populus tremula Populus tremuloides PsRBR1 PsRBR1 PsRBR1 PsRBR1 Interactions of PsRBR1 protein with both plant D-type cyclins and a mammalian oncoprotein 1 Arabidopsis 1998 1995 Table 1 PsRBR1 protein binding in the two-hybrid assay a b PsRBR1 0.11 ± 0.01 PsRBR1  Pissa;CycD3;1 13.9 ± 0.2 PsRBR1 + Arath;CycD3;1 10.6 ± 0.1 PsRBR1 SV 40 large-T antigen 31.5 ± 0.1 a Saccharomyces cerevisiae b O O d Immunochemical detection of PsRBR1 protein in pea axillary buds 2 2 2 2 Fig. 2 A B PsRBR1 35 PsRBR1 C  Comparison of molecular mass of authentic PsRBR1 protein in pea with that of in vitro-synthesized PsRBR1 protein PsRBR1 2 35 2 PsRBR1 PsRBR1 2 2 2 Dephosphorylation of authentic PsRBR1 protein 1998 1999 1 2 2 2002 2 2 2 Protein levels and phosphorylation states of PsRBR1 protein in axillary buds during dormancy-to-growth transition 3 3 3 PsRBR1 3 Fig. 3 A B PsRBR1 PCNA histone H4  PsRBR1 PsRBR1 PCNA Histone H4 PsRBR1 PCNA histone H4 1998 3 PsRBR1 PsRBR1 histone H4 Histone H4 PsRBR1 histone H4 PsRBR1 3 PsRBR1 PCNA PCNA PCNA Detection of phosphorylated PsRBR1 protein in axillary buds after decapitation 4 32 4 32 4 32 4 Fig. 4 A 32 32 B 32 A  4 4 4 Discussion In intact plants, the pea shoot apex inhibits growth; i.e., cell elongation and cell division of the dormant axillary buds. The cell cycle of dormant axillary buds is arrested at the G1 phase. Therefore, from the point of view of cell cycle control, the transition from dormancy to outgrowth in axillary buds seems to be from the G1 phase to the S phase. In animal cells, RB family proteins function as negative controllers in G1 arrest, and the activities of RB family proteins are controlled by their phosphorylation states. Here, we investigated phosphorylation states of the pea RB-related protein, PsRBR1, during the dormancy-to-growth transition in axillary buds. The results of the present study provide a basis for further studies of the molecular mechanisms underlying apical dominance and cell cycle control. 1998 1999 1999 1996 1999 Drosophila melanogaster Zea mays Nicotiana tabacum Chenopodium rubrum Arabidopsis thaliana Populus tremula Populus tremuloides Cocos nunucifera Oryza sativa 1999 1996 2000 1999 1996 Arabidopsis thaliana Oryza sativa RB PsRBR1 RB RB 2005 3 2002 1996 1998 1996 1999 1999 PCNA 1991 PCNA PCNA PCNA PCNA 2001 1993 1997 1995 Arabidopsis D-type cyclin 1995 2006 D-type cyclin