In eudicotyledonous model plants, the B-function genes encode a pair of partner MADS-domain proteins, APETALA3 (AP3) and PISTILLATA (PI) in Arabidopsis and DEFICIENS (DEF) and GLOBOSA (GLO) in Antirrhinum. These proteins, which must form heterodimers to function, are required to specify petal and stamen identity during flower development. Here, we report cloning and characterization of TrPI (Taihangia rupestris PISTILLATA), a PI/GLO-like gene from the core eudicot species Taihangia rupestris (Rosaceae). DNA gel blot analysis showed that TrPI is a single copy gene in the T. rupestris genome. Quantitative RT-PCR and in situ hybridization analyses revealed that TrPI is transcribed in both the vegetative and reproductive organs at different levels. Ectopic expression of TrPI in Arabidopsis caused severe modifications in vegetative plant architecture, including rosette leaves and cauline leaves arranged in a non-spiral phyllotaxy, and a flattened primary inflorescence stem that produced two or three offshoots at the base, middle or top. Moreover, we show that the TrPI gene is capable of rescuing pi-1 mutant phenotypes. Yeast two-hybrid assays showed that TrPI forms homodimers. Taken together, these results show that TrPI might function in regulating plant architecture in addition to its function as a floral organ identity gene in T. rupestris, suggesting that the TrPI protein has biochemical features that distinguish it from the well-studied orthologs, PI and GLO. (C) 2010 Elsevier GmbH. All rights reserved.