Genetic interaction between glabra3-shapeshifter and siamese in Arabidopsis thaliana converts trichome precursors into cells with meristematic activity

The identity of many genes required for trichome differentiation is known. This paper describes a novel interaction between mutant alleles of two such genes. One of the alleles, called gl3-sst, is derived from the GL3 locus, which encodes a basic helix-loop-helix type transcription factor. The mutation in the gl3-sst protein modifies its ability to form a complex with the GL1 protein (a MYB transcription factor required for trichome formation), leading to changes in gene expression compared with wild type during gl3-sst mutant trichome development. The other mutant allele, sim, is a likely loss of function allele derived from the SIM locus, which is predicted to encode a negative regulator of D-type cyclin activity. The gl3-sst sim double mutant exhibits mounds of cells derived from the proliferation of single trichome precursors. The ectopic expression of a D-type cyclin gene in gl3-sst mimics the double mutant phenotype. Thus, an interaction between altered trichome gene expression caused by the gl3-sst mutation and relaxed regulation of D-type cyclin activity in the double mutant converted a non-dividing cell into a novel highly proliferating cell type.