Enhancement of meristem formation by bouquet-1, a mis-sense allele of the VERNALIZATION INDEPENDENCE 3 gene encoding a WD40 repeat protein in Arabidopsis thaliana

In higher plants, the shoot apical meristem (SAM) is the ultimate source supplying cells that constitute the aboveground tissues and organs. The cells supplied from the SAM begin to proliferate rapidly and then concomitantly start to differentiate. We identified a novel mutant, named bouquet-1 (boq-1), exhibiting highly pleiotropic shoot growth phenotypes. The boq-1 plants showed an increase in the inflorescence stem number accompanied by frequent fasciation. This particular phenotype appeared to be due to the development of extra SAMs in a SHOOT MERISTEMLESS (STM)-dependent manner. Expression of STM was also expanded widely in the boq-1 shoot apex, suggesting that the repressive state of the STM transcription may not be established or maintained, leading to the misexpression. Molecular cloning of the relevant gene showed that the BOQ gene encodes a WD40 repeat protein, which has been reported as VERNALIZATION INDEPENDENCE 3 (VIP3). In addition, the finding that overproduction of the boq-1 allele in the wild-type background mimicked the boq-1 phenotypes in a dose-dependent manner suggested that the mutant BOQ-1 protein acts in a dominant negative manner. Taking these results together, we propose that the boq-1 mutation affects the proper progression of cell differentiation process.