Posttranscriptional Regulation of RhBRC1 (Rosa hybrida BRANCHED1) in Response to Sugars is Mediated via its Own 3′ Untranslated Region, with a Potential Role of RhPUF4 (Pumilio RNA-Binding Protein Family)

Abstract : The shoot branching pattern is a determining phenotypic trait throughout plant development. During shoot branching, BRANCHED1 (BRC1) plays a master regulator role in bud outgrowth, and its transcript levels are regulated by various exogenous and endogenous factors. RhBRC1 (the homologous gene of BRC1 in Rosa hybrida) is a main branching regulator whose posttranscriptional regulation in response to sugar was investigated through its 3 ' UTR. Transformed Rosa calluses containing a construction composed of the CaMV35S promoter, the green fluorescent protein (GFP) reporter gene, and the 3 ' UTR of RhBRC1 (P35S:GFP::3 ' UTRRhBRC1) were obtained and treated with various combinations of sugars and with sugar metabolism effectors. The results showed a major role of the 3 ' UTR of RhBRC1 in response to sugars, involving glycolysis/the tricarboxylic acid cycle (TCA) and the oxidative pentose phosphate pathway (OPPP). In Rosa vegetative buds, sequence analysis of the RhBRC1 3 ' UTR identified six binding motifs specific to the Pumilio/FBF RNA-binding protein family (PUF) and probably involved in posttranscriptional regulation. RhPUF4 was highly expressed in the buds of decapitated plants and in response to sugar availability in in-vitro-cultured buds. RhPUF4 was found to be close to AtPUM2, which encodes an Arabidopsis PUF protein. In addition, sugar-dependent upregulation of RhPUF4 was also found in Rosa calluses. RhPUF4 expression was especially dependent on the OPPP, supporting its role in OPPP-dependent posttranscriptional regulation of RhBRC1. These findings indicate that the 3 ' UTR sequence could be an important target in the molecular regulatory network of RhBRC1 and pave the way for investigating new aspects of RhBRC1 regulation.